Semiconductor display device and method of manufacturing the same

ABSTRACT

A semiconductor display device with an interlayer insulating film in which surface levelness is ensured with a limited film formation time, heat treatment for removing moisture does not take long, and moisture in the interlayer insulating film is prevented from escaping into a film or electrode adjacent to the interlayer insulating film. A TFT is formed and then a nitrogen-containing inorganic insulating film that transmits less moisture compared to organic resin film is formed so as to cover the TFT. Next, organic resin including photosensitive acrylic resin is applied and an opening is formed by partially exposing the organic resin film to light. The organic resin film where the opening is formed, is then covered with a nitrogen-containing inorganic insulating film which transmits less moisture than organic resin film does. Thereafter, the gate insulating film and the two layers of the nitrogen-containing inorganic insulating films are partially etched away in the opening of the organic resin film to expose the active layer of the TFT.

This application is Division of U.S. application Ser. No. 11/151,260Filed Jun. 14, 2005 now U.S. Pat. No. 7,148,510, now Issued, which is aDivision of U.S. application Ser. No. 10/412,687, Filed Apr. 14, 2003now U.S. Pat. No. 6,911,688, now Issued.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor display device whichuses an organic resin film as an interlayer insulating film, and morespecifically to a semiconductor display device structured which has aprotective circuit formed in an input/output portion to protect internalcircuits against breakage brought by high voltage load such as staticelectricity.

2. Description of the Related Art

In recent years, a technique of forming a TFT on a substrate has greatlyprogressed, and its application and development for an active matrixsemiconductor display device as one of the semiconductor devices havebeen advanced. In particular, since a TFT using a polycrystallinesemiconductor film has higher field-effect mobility (also referred to asmobility) than a conventional TFT using an amorphous semiconductor film,it enables high-speed operation. It is therefore possible to control thepixel by the driver circuit formed on the same substrate where the pixelis formed, though the pixel is conventionally controlled by a drivercircuit provided outside the substrate.

A TFT consists of an active layer obtained by adding impurities toimpart one conductivity type on a semiconductor film, a gate electrode,and a gate insulating film formed between the active layer and the gateelectrode. Further, generally, an interlayer insulating film comprisedof an insulating film is formed to cover the TFT, and the wiring to beelectrically connected to the TFT on the interlayer insulating film isformed on the interlayer insulating film.

In a case where a wiring to be electrically connected to the TFT isformed on the interlayer insulating film, if the surface of theinterlayer insulating film is not leveled sufficiently, the wiring willbe broken or, though the wiring is not totally broken and locallythinned, the wiring resistance will increase. In addition to the wiring,if a pixel electrode is formed on the interlayer insulating film, thesurface irregularities in the interlayer insulating film cause thesurface irregularities in the pixel electrode and the inequalitythickness of the pixel electrode. This may result in unevenness in adisplayed image.

It is therefore necessary to give the interlayer insulating film enoughthickness, 1 to 5 μm for example, so that the shape of the TFT does notcause the surface irregularities in the interlayer insulating film.

Films for use as the interlayer insulating film are roughly divided intoinsulating films formed of inorganic materials (hereafter referred to asinorganic insulating films) and insulating films formed of insulativeorganic resin (hereinafter referred to as organic resin films).

An inorganic insulating film is formed using vapor phase growth methodsuch as CVD method and sputtering method. Using an inorganic insulatingfilm as the interlayer insulating film has a drawback because it takestime to form a film thick enough to level the surface using vapor phasegrowth method.

On the other hand, if an organic resin film is used, the interlayerinsulating film is formed by applying organic resin to a substrate onwhich the TFT is formed, and therefore a leveled surface is easilyobtained.

The wiring to be connected to the TFT is obtained by forming a filmhaving conductivity (hereinafter referred to as conductive film) on theinterlayer insulating film in which a contact hole is opened and thenetching the conductive film.

The conductive film can be etched either by wet etching or dry etching.Wet etching is isotropic etching and therefore is not adaptable towiring pattern miniaturization if it goes beyond 3 μm. Dry etching, onthe other hand, is anisotropic etching and therefore can deal withwiring pattern miniaturization.

However, a problem of dry etching is that, when the conductive film onan organic resin film serving as the interlayer insulating film istreated by dry etching, the surface of the organic resin film isroughen. With the surface of the organic resin film roughened, aflatness of the pixel electrode formed on the organic resin film isimpaired and pixel display is accordingly affected.

Organic resin has high water-absorbing property and swells with water inan alkaline aqueous solution which is used in development. Therefore, adehydration step of extracting water from the organic resin film by heattreatment has to be included after development. Despite dehydrationthrough heat treatment, the organic resin film absorbs moisture in theadjacent films or in the air. There is a fear that the absorbed moisturecorrodes over time the wiring that is in contact with the organic resinfilm and impairs the long-time reliability of the panel.

SUMMARY OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide a semiconductor display device with an interlayer insulatingfilm in which surface levelness is ensured with a limited film formationtime, heat treatment for removing moisture does not take long, andmoisture in the interlayer insulating film is prevented from escapinginto a film or electrode adjacent to the interlayer insulating film.

Research by the applicant of the present invention shows a fact that,when a resin film is used as an interlayer insulating film and a contacthole is formed using dry etching, thin film transistors obtained arelargely fluctuated in threshold voltage (Vth). The data obtained can bemade into a graph through estimation by statistical work of thresholdvoltage fluctuation, in which the horizontal axis shows the channellength (how far carriers move) and the vertical axis shows the Vthfluctuation. In recent years, statistical work called ‘quartiledeviation’ becomes widely recognized. Quartile deviation shows thedifference between the 25% value and the 75% value in normal probabilitygraph and is noticed as statistical work that is not influenced bypeculiar values. Based on quartile deviation, the applicants of thepresent invention have defined the difference between the 16% value andthe 84% value as 16% quantile deviation and plotted it into the verticalaxis as ‘Vth fluctuation’. The 16% quantile deviation corresponds to ±σin normal probability distribution and therefore data plot used isobtained by multiplying each by a coefficient to make them into. valuesdeemed as ±3σ. According to the data, the fluctuation is about 4 times(in n-channel TFTs) or twice (in p-channel TFTs) larger when an acrylicfilm is used as the interlayer insulating film. It is obviously that theuse of the acrylic film increases the fluctuation. The applicants of thepresent invention infer that the threshold voltage fluctuation is causedby electric charges trapped in the acrylic film due to plasma damagereceived during dry etching.

The present invention has been made in view of the above problems, andan oject of the present invention is therefore to provide a technique ofbuilding thin film transistors in manufacturing a semiconductor displaydevice that uses an organic resin film as an interlayer insulating filmwithout allowing the threshold voltage to fluctuate among the thin filmtransistors, thereby improving the stability of the operationperformance of the display device and enlarging the design margin incircuit design. Another object of the present invention is to improvethe image quality. of the display device.

In the present invention, an organic resin film containing a positivephotosensitive acrylic resin is surrounded by a nitrogen-containinginsulating film that transmits less moisture compared to organic resinfilm.

Specifically, a TFT is formed and then a nitrogen-containing inorganicinsulating film that transmits less moisture compared to organic resinfilm is formed so as to cover the TFT. Next, organic resin includingphotosensitive acrylic resin is applied and an opening is formed bypartially exposing the organic resin film to light. The organic resinfilm where the opening is formed is then covered with anitrogen-containing inorganic insulating film that transmits lessmoisture than organic resin film does. Thereafter, the gate insulatingfilm and the two layers of the nitrogen-containing inorganic insulatingfilms are partially etched away in the opening of the organic resin filmto expose the active layer of the TFT.

What is important in this etching is to avoid exposure of the organicresin film in region where a wiring, a pixel electrode, or the like isformed not to be affected by moisture and by surface irregularities in alater step. The organic resin film may also be covered with an inorganicinsulating film completely in the rest of the region.

In general, inorganic insulating films receive less etching damage indry etching compared to organic resin films represented by acrylic resinfilms and accordingly the surface is roughened less. The pixel electrodeor the like that is formed later is therefore saved from surfaceirregularities and uneven thickness, thereby preventing uneven display.

Covering the organic resin film with the nitrogen-containing inorganicinsulating film that transmits less moisture compared to the organicresin does also prevents the organic resin film from releasing moisturecontained within. Also this prevents the organic resin film fromswelling with water in an alkaline aqueous solution which is used indevelopment and thus saves heat treatment time for removal of moistureafter development. Accordingly, moisture in the organic resin film isfurther prevented from escaping into a film or electrode adjacent to theorganic resin film and the long-term reliability of the panel isenhanced. Moreover, in the case of a light emitting device which uses alight emitting element represented by an organic light emitting diode(OLED), it prevents degradation in luminance of the light emittingelement due to moisture released from the organic resin film.

Covering the entire organic resin film with an inorganic insulating filmto leave no region exposed further prevents the organic resin film fromswelling with water in the alkaline aqueous solution which is used indevelopment and thus save heat treatment time for removal of moistureafter the development. Accordingly, moisture in the organic resin filmis further prevented from escaping into a film or electrode adjacent tothe organic resin film and the long-term reliability of the panel isenhanced.

In the present invention, photosensitive acrylic resin is used for theorganic resin film. Photosensitive organic resin is classified into apositive type and a negative. type; if a portion of a resin film that isexposed to energy beam such as photo, electron and ion is removed, it isthe positive type, and if the exposed portion remains whereas the restis removed, it is the negative type.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D show sectional views of photosensitive acrylic films inopenings.

FIG. 2 shows a sectional view of a photosensitive positive polyimidefilm in an opening.

FIGS. 3A to 3C show sectional views of a contact hole.

FIGS. 4A to 4D show diagrams showing the positional relation between acontact hole and a wiring.

FIGS. 5A and 5B show sectional views of a TFT and capacitor storage of asemiconductor display device of the present invention.

FIG. 6 shows a block diagram of driving circuits in a semiconductordisplay device of the present invention.

FIG. 7 shows a circuit diagram of a protective circuit.

FIGS. 8A and 8B show diagrams showing the operation of a protectivecircuit.

FIGS. 9A and 9B show timing charts of clock signals.

FIG. 10 shows a circuit diagram of a protective circuit.

FIG. 11 shows a mask draft for a protective circuit.

FIG. 12 shows a sectional view of capacitor storage of a protectivecircuit.

FIGS. 13A to 13C show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 14A to 14C show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 15A to 15C show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 16A to 16C show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 17A and 17B show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 18A and 18B show block diagrams showing the structure of asemiconductor display device of the present invention and a circuitdiagram of a pixel portion.

FIG. 19 shows a circuit diagram of a buffer, a scanning line, andcapacitor storage.

FIGS. 20A and 20B show a mask draft for a buffer and capacitor storageand a sectional view of the capacitor storage.

FIGS. 21A to 21D show sectional views of a semiconductor display deviceof the present invention.

FIGS. 22A and 22B show sectional views of a semiconductor display deviceof the present invention.

FIGS. 23A and 23B show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIG. 24 shows a top view of a semiconductor display device of thepresent invention.

FIG. 25 shows a sectional view of a semiconductor display device of thepresent invention.

FIG. 26 shows a block diagram of driving circuits in a semiconductordisplay device of the present invention.

FIGS. 27A to 27H show diagrams showing electronic apparatuses using asemiconductor display device of the present invention.

FIGS. 28A and 28B show sectional views of a semiconductor display deviceof the present invention.

FIG. 29 shows diagrams showing the relation between the channel lengthand threshold of TFTs.

FIGS. 30A and 30B show diagrams showing the C-V characteristic of TFTs.

FIGS. 31A and 31B show sectional views of a non-photosensitive acrylicfilm in an opening.

FIGS. 32A and 32B show sectional views of a positive photosensitiveacrylic film in an opening.

FIGS. 33A and 33B show sectional views of a negative photosensitiveacrylic film in an opening.

FIGS. 34A and 34B show sectional views of a positive photosensitivepolyimide film in an opening.

FIGS. 35A to 35C show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 36A to 36C show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 37A to 37D show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

FIGS. 38A to 38D show diagrams showing a method of manufacturing asemiconductor display device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Sectional views of an opening in positive acrylic resin and an openingin negative acrylic resin are shown in FIGS. 1A to 1D. In the case ofpositive acrylic resin, as shown in FIG. 1A, a first inorganicinsulating film 7000 is formed before a positive acrylic organic resinfilm is formed and then a portion of the organic resin film where anopening is to be formed is exposed to light. Thereafter, the portionexposed to light is removed through development to expose the firstinorganic insulating film 7000. Then a second inorganic insulating film7002 is formed so as to cover the positive organic resin film with theopening (the film being denoted by 7001) and the exposed portion of thefirst inorganic insulating film 7000.

FIG. 1B shows an enlarged view of the section of the positive organicresin film 7001 with the opening. As shown in FIG. 1B, the opening insection forms a curve. Tangent lines of the curve at points on thesurface of the positive organic resin film 7001 are slanted with respectto the substrate direction (horizontal direction) and the slant becomessmaller as the distance from the opening is increased. In other words,the radius of curvature measured at each of the contact points R1, R2,and R3 becomes continuously longer as the distance from the opening isincreased, thereby describing a parabola that has its principal axis ina plane parallel to the substrate. For instance, the minimum radius ofcurvature at an end of a positive photosensitive acrylic film isapproximately 3 to 30 μm, although depending on exposure conditions. Ateach of the contact points R1, R2, and R3, all the center of curvatureare on the side of the positive organic resin film 7001 (substrateside).

When using positive acrylic, an angle θ of the tangent line at thecontact point where the positive organic resin film 7001 fades into theopening can be set equal to or larger than 30° and equal to or smallerthan 65° with respect to the substrate.

As described, in the case of a positive organic resin film, all thecenters of curvature of the surface of the organic resin film in theopening are on the substrate side and there is little chance thatdefective etching leaves a part of the film in the portion that needs tobe opened. Accordingly, less contact defects are caused and the yield isimproved.

In the case of negative acrylic resin, as shown in FIG. 1C, a firstinorganic insulating film 7005 is formed before a negative acrylicorganic resin film is formed and then a portion of the organic resinfilm except a part where an opening is to be formed is exposed to light.Thereafter, the portion not exposed to light is removed throughdevelopment to expose the first inorganic insulating film 7005. Then asecond inorganic insulating film 7007 is formed so as to cover thenegative organic resin film 7006 where the opening is formed and theexposed portion of the first inorganic insulating film 7005.

FIG. 1D is an enlarged view of the section of the negative organic resinfilm 7006 with the opening. As shown in FIG. 1D, the opening in sectionforms a curve. Tangent lines of the curve at points on the surface ofthe negative organic resin film 7006 are slanted with respect to thesubstrate direction (horizontal direction) and the slant becomes smalleras the distance is increased away from a contact point R0 in theopening. In other words, the radius of curvature measured at contactpoints R1, R2, and R3 becomes continuously longer as the distance fromthe contact point R0 is increased leaving the opening. Toward the centerof the opening from the contact point R0, the slant of the tangent linebecomes small and the radius of curvature is continuously increased. Atthe contact points R1, R2, and R3 outside of the contact point R0 in theopening, the center of curvature is on the side of the negative organicresin film 7006 (the substrate side). At a contact point R-1 that isbetween the contact point R0 and the center of the opening, the centerof curvature is on the side opposite to the negative organic resin film7006 (the side opposite to the substrate).

As described, in the case of a negative organic resin film, the centerof curvature of the surface of the organic resin film from the contactpoint R0 toward the center of the opening is on the side opposite to thesubstrate. The longer the distance from the contact point R0 to a pointwhere the negative organic resin film 7006 ceases, the smaller the areaof the opening becomes and the higher the possibility of defectivecontact rises. The distance is changed by changing etching conditionsand the thickness of the organic resin film before the opening isformed. FIG. 1 show the case of acrylic resin as an example. In the caseof using a film of organic resin other than acrylic resin, thecomposition of the resin also changes the distance from the contactpoint R0 to the point where the organic resin film 7006 ceases.Therefore, negative photosensitive organic resin which forms thesectional shape shown in FIGS. 1C and 1D is made employable if thedistance from the contact point R0 to the point where the negativeorganic resin film 7006 ceases is shortened to a length that ensuresenough area for the opening, for example, about 1 μm.

Still, as a part of an interlayer insulating film, organic resin thatcan form the sectional shape shown in FIGS. 1A and 1B is preferred toorganic resin which forms the sectional shape shown in FIGS. 1C and 1D.However, not all of positive photosensitive organic resin can form thesectional shape shown in FIGS. 1A and 1B; positive acrylic can form thesectional shape shown in FIGS. 1A and 1B whereas positive polyimide cannot.

When using non-photosensitive organic resin, commonly dry etching isused to form an opening in the interlayer insulating film. Dry etchingis an etching method that uses plasma of active radical or reactive gas.The interlayer insulating film is ten times as thick as a gateinsulating film, and dry etching to form an opening therein takes time,keeping the process object exposed to plasma that much longer. If asubstrate on which a TFT is formed is exposed to plasma for a longperiod of time, the TFT threshold is easily fluctuated toward the plusside because of so-called charging damage in which holes are trapped ina gate insulating film. By employing photosensitive organic resin andusing wet etching to form an opening as in the present invention, thedry etching period is significantly shortened and fluctuation of TFTthreshold is therefore prevented.

Furthermore, in the present invention, a gate electrode of a TFT and oneelectrode of a capacitor used in a driving circuit of a semiconductordisplay device are formed at the same time whereas a wiring electricallyconnected to the TFT and the other electrode of the capacitor are formedat the same time. Then two layers of inorganic insulating films in theopening of the organic resin film overlap each other and are sandwichedbetween two electrodes to form capacitor storage.

This capacitor storage is used in a protective circuit of thesemiconductor display device of the present invention.

Static electricity generated by friction or other causes reaches as highvoltage as several tens V, even several tens kV in some cases. When ahuman or object electrified touches a semiconductor display device, thecharges may be discharged at once in as short a period as several μs toseveral ms through an input terminal, wiring, or circuit of thesemiconductor display device. Such rapid electric discharge coulddegrade or break a very thin gate insulating film and a TFT or othersemiconductor element with a very short channel length, which are usedin circuits of the semiconductor display device.

In addition, noise is sometimes contained at a given frequency in aclock signal or the like that an input terminal of a semiconductordisplay device receives. The noise gives a voltage higher or lower thana desired voltage to a semiconductor element in an instant, therebycausing malfunction of the semiconductor element. In case ofsemiconductor display devices in particular, the noise can result indisturbed images.

The present invention uses the above capacitor storage for a capacitorof a protective circuit that protects a semiconductor element fromdegradation or damage caused by static electricity discharge andprevents malfunction of a semiconductor element due to noise. With theabove structure, the protective circuit can readily be built on the samesubstrate where a pixel portion is formed, degradation or breakage of asemiconductor element by static electricity is prevented, andmalfunction by noise is avoided to prevent disturbed images.

FIG. 2 shows an enlarged view of the section in an opening when apositive photosensitive polyimide is employed. Similar to the case wherepositive acrylic is used, a positive polyimide film is formed after afirst inorganic insulating film 7010 is formed as shown in FIG. 2. Aportion where the opening is to be formed is exposed to light anddeveloped to form the opening, thereby exposing the first inorganicinsulating film 7010. Then a second inorganic insulating film 7012 isformed so as to cover the positive polyimide film with the opening (thefilm being denoted by 7011) and the exposed portion of the firstinorganic insulating film 7010.

As to the positive polyimide film 7011 with the opening, an end of thefilm is not sufficiently rounded in the opening. This makes a wiringthin when formed on the second inorganic insulating film 7012 at theend, and then the wiring resistance is increased. On the other hand, theinsufficiently rounded end of the positive polyimide film 7011 in theopening may cause the second inorganic insulating film 7012 on an edge7013 to be thicker than the rest when the second inorganic insulatingfilm 7012 is formed by vapor phase growth. This is because molecules ofthe material that constitutes the thin film move, upon landing on asurface to be coated, over the surface seeking for a stable site andtend to gather in a portion shaped to have a sharp angle (a convexshape) such as an upper edge of a contact hole. This tendency isparticularly notable in evaporation. When the thickness of the secondinorganic insulating film 7012 is partially increased at the edge 7013,the wiring is thinned particularly at the end to bring an increase inwiring resistance.

Consequently, it is not preferable to use as a part of an interlayerinsulating film of the present invention, positive photosensitivepolyimide or other organic resin that does not form a curve at an end inthe opening as the sectional shape shown in FIG. 2.

Next a description is given on the section near a contact hole which isopened by etching an inorganic insulating film. After the state shown inFIG. 1A is reached, a resist mask 7021 is formed and a contact hole 7023is formed by dry etching of the first inorganic insulating film 7000,the second inorganic insulating film 7002, and a gate insulating film7022, which is formed between the first inorganic insulating film and asemiconductor film, as shown in FIG. 3A.

FIG. 3B shows the vicinity of the contact hole viewed from above thesubstrate after the resist mask 7021 is removed for clearer view. Asectional view taken along the line A-A′ in FIG. 3B corresponds to FIG.3A.

The contact hole 7023 is formed in the opening 7024, which is formed inthe positive organic resin film 7001. Then a conductive film 7025 isformed on the second inorganic insulating film 7002 to cover the contacthole 7023 as shown in FIG. 3C. The conductive film 7025 is patterned toform a wiring.

FIG. 4 shows the positional relation between the wiring, the opening7024 of the positive organic resin film 7001 and the contact hole 7023respectively. FIG. 4A is a top view showing the vicinity of the contacthole 7023. FIG. 4B is a sectional view taken along the line A-A′ in FIG.4A.

The wiring 7026 obtained by patterning the conductive film 7025 isconnected through the contact hole 7023 that is formed about the centerof the opening 7024 to a semiconductor film 7300 which is formed underthe gate insulating film 7022.

As described, the contact hole 7023 has to be confined within theopening 7024 in order to avoid exposing the positive organic resin film7001 in the contact hole 7023 after the contact hole 7023 is formed.

The contact hole 7023 in FIGS. 4A and 4B is positioned about the centerof the opening 7024, but the present invention is not limited to thisstructure. The contact hole 7023 may be off the center of the opening7024 as long as it is confined within the opening 7024.

FIG. 4C is a top view showing the vicinity of the contact hole 7023 inthe case where the contact hole 7023 is off the center of the opening7024. FIG. 4D is a sectional view taken along the line B-B′ in FIG. 4C.

The wiring 7026 obtained by patterning the conductive film 7025 isconnected to the semiconductor film (not shown in the drawing) formedunder the gate insulating film 7022 through the contact hole 7023 thatis in an upper part of the opening 7024 in the drawing.

FIGS. 4A to 4D show contact between the wiring and the semiconductorfilm and the same applies to contact between the wiring and a gateelectrode.

Next, a description will be given with reference to FIG. 5 on thestructure of a TFT and a capacitor in a semiconductor display device ofthe present invention.

In FIG. 5A, a TFT 8001 is formed on an insulating surface 8000. The TFT8001 is of top gate type, and has a semiconductor film 8002, a gateinsulating film 8003 that is in contact with the semiconductor film8002, and a gate electrode 8004 that is in contact with the gateinsulating film 8003. The semiconductor film 8002 is in contact with theinsulating surface 8000. The semiconductor film 8002 has a channelformation region 8005 and impurity regions 8006 that sandwich thechannel formation region 8005.

A first capacitor electrode 8007 is formed on the gate insulating film8003 from a conductive film that is used to form the gate electrode8004.

A first inorganic insulating film 8008 is formed so as to cover the TFT8001 and the first capacitor electrode 8007. The first inorganicinsulating film 8008 is an insulating film containing nitrogen andtransmits less moisture than an organic resin film which is formed laterdoes.

Photosensitive organic resin is applied to the top face of the firstinorganic insulating film 8008 and baked. A portion of the resin filmwhere an opening is to be formed is exposed to light and developed toobtain an organic resin film 8009 with an opening. At this point, a partof the first inorganic insulating film 8008 is exposed in the opening.

A second inorganic insulating film 8010 is formed to cover the organicresin film 8009 and the portion of the first inorganic insulating film8008 that is exposed in the opening. The second inorganic insulatingfilm 8010 is, similar to the first inorganic insulating film 8008, aninsulating film containing nitrogen and transmits less moisture than anorganic resin film which is formed later does.

The first inorganic insulating film 8008 and the second inorganicinsulating film 8010 are used as dielectric of capacitors. Therefore, ifthe first and second inorganic insulating films are too thick, thecapacitance value of the capacitors is reduced and treatment time forforming the films is prolonged. On the other hand, too thin first andsecond inorganic insulating films have only a small degree of effect inpreventing permeation of moisture. Preferably, the first inorganicinsulating film 8008 and the second inorganic insulating film 8010 eachhave a thickness of about 10 to 200 nm and the total thickness of thetwo layers is preferably about 20 to 400 nm.

A contact hole is formed by dry etching through the gate insulating film8003, the first inorganic insulating film 8008, and the second inorganicinsulating film 8010 so that a part of the semiconductor film is exposedin the opening of the organic resin film 8009. During the dry etching,the semiconductor film 8002 serves as an etching stopper.

The first inorganic insulating film 8008 and the second inorganicinsulating film 8010 existing above the first capacitor electrode 8007are kept covered with a resist mask in order to avoid being etchedduring the dry etching.

The resist mask is then removed using a developer. A developer ingeneral is an alkaline aqueous solution and contains a large amount ofmoisture. In the present invention, the organic resin film 8009 iscovered with the first inorganic insulating film 8008 and the secondinorganic insulating film 8010 to avoid direct exposure to a developer.Therefore, moisture in the developer is mostly prevented from enteringthe organic resin film 8009 and hardly causes swelling. Accordingly,heat treatment for removal of moisture after the resist mask is removedusing the developer can be finished in a shortened period of time.

Then a conductive film is formed on the second inorganic insulating film8010 so as to cover the contact hole. The conductive film is etched toform a wiring 8011 which is connected to the semiconductor film 8002,and the second capacitor electrode 8012. The second capacitor electrode8012 overlaps the first capacitor electrode 8007 sandwiching between thefirst inorganic insulating film 8008 and the second inorganic insulatingfilm 8010. The second capacitor electrode 8012, the first inorganicinsulating film 8008, the second inorganic insulating film 8010, and thefirst capacitor electrode 8007 form capacitor storage 8013.

The present invention is characterized by using this capacitor storage8013 as a capacitor included in a protective circuit of thesemiconductor display device. Also, the transistor structured in theprotective circuit is used as a TFT of the protective circuit as above.

As the end of the opening in the organic resin film 8009 is more gentlycurved in section, the gate electrode comes nearer to the end of theopening. However, the gate electrode is prevented from touching thewiring or the like formed in the opening even when the gate electrodepushes up through the end of the opening and is exposed because thesecond inorganic insulating film is formed on the organic resin film8009 in the present invention.

The TFT 8001 may either be of top gate type or bottom gate type.

In addition to the capacitor storage of FIG. 5A, capacitor storage maybe formed between the semiconductor film and the first capacitorelectrode 8007. FIG. 28A shows an example in which first capacitorstorage 8053 is formed by overlapping a capacitor semiconductor film8050 and a first capacitor electrode 8051 with a gate insulating film8052 interposed therebetween. Similar to FIG. 5A, second capacitorstorage 8057 is formed by overlapping the first capacitor electrode 8051and a second capacitor electrode 8054 with a first inorganic insulatingfilm 8055 and a second inorganic insulating film 8056 interposedtherebetween. By forming upper capacitance and lower capacitance asthis, a higher capacitance value is obtained using the same area.

Alternatively, a so-called dual gate TFT may be employed in which twogate electrodes overlap each other with a channel formation regionsandwiched therebetween. FIG. 28B is a sectional view of a semiconductordevice using a dual gate TFT. A TFT 8600 has a first gate electrode8601, a first gate insulating film 8602, a semiconductor film 8603, asecond gate insulating film 8604, and a second gate electrode 8605. Thefirst gate electrode 8601 overlaps a channel formation region 8606 ofthe semiconductor film 8603 with the first gate insulating film 8602interposed between the two. The second gate electrode 8605 overlaps thechannel formation region 8606 with the second gate insulating film 8604sandwiched therebetween. Moreover the first gate electrode 8601 and thesecond gate electrode 8605 overlap sandwiching the channel formationregion 8606.

If the same level of voltage is applied to the first gate electrode andthe second gate electrode, a depletion layer spreads as fast as when thesemiconductor film is actually thinned. Therefore, the sub-thresholdcoefficient (S value) can be reduced while the ON current is raised.Furthermore, interface scatter can be reduced and the trans-conductance(gm) is increased. By applying a common voltage to the first or secondgate electrode, the threshold fluctuation is reduced compared to thecase in which there is only one electrode and OFF current can be reducedas well.

The first gate insulating film 8602 is in contact with a first capacitorelectrode 8610 that is formed from the same conductive film as the firstgate electrode 8601. The second gate insulating film 8604 is in contactwith the first gate insulating film. A second capacitor electrode 8611is formed from the same conductive film as the second gate electrode8604 and is in contact with the second gate insulating film. The firstcapacitor electrode 8610 and the second capacitor electrode 8611 overlapeach other with the first gate insulating film 8602 and the second gateinsulating film 8604 interposed therebetween, and first capacitorstorage 8612 is formed in the portion where these electrodes overlap.

The second capacitor electrode 8611 is in contact with a first inorganicinsulating film 8614 in an opening of an organic resin film 8613. Asecond inorganic insulating film 8615 is formed so as to have a contactwith the first inorganic insulating film 8614. A third capacitorelectrode 8616 is formed so as to have a contact with the secondinorganic insulating film 8615. The second capacitor electrode 8611 andthe third capacitor electrode 8616 overlap each other with the firstinorganic insulating film 8614 and the second inorganic insulating film8615 interposed therebetween, and second capacitor storage 8617 isformed in the portion where these electrodes overlap. By forming anupper capacitor and a lower capacitor as this, the capacitance valueobtained from the same area is increased.

FIG. 5B shows the structure of a semiconductor display device of thepresent invention which uses a bottom gate TFT.

In FIG. 5B, a TFT 8101 is formed on an insulating surface 8100. The TFT8101 is of bottom gate type, and has a semiconductor film 8102, a gateinsulating film 8103 that is in contact with the semiconductor film8102, and a gate electrode 8104 that is in contact with the gateinsulating film. The gate electrode 8104 is in contact with theinsulating surface 8100. The semiconductor film 8102 has a channelformation region 8105 and impurity regions 8106 that sandwich thechannel formation region. Denoted by 8115 is an insulating film used asa mask when the semiconductor film is doped with an impurity, and theinsulating film is called here as a channel protecting film.

A first capacitor electrode 8107 is formed on the insulating surface8100 from the same conductive film as the gate electrode 8104.

A first inorganic insulating film 8108 is formed so as to cover the TFT8101 and the first capacitor electrode 8107. Then photosensitive organicresin is applied to the top face of the first inorganic insulating filmand baked. A portion of the resin film where an opening is to be formedis exposed to light and developed to obtain an organic resin film 8109with an opening. At this point, a part of the first inorganic insulatingfilm 8108 is exposed in the opening.

A second inorganic insulating film 8110 is formed to cover the organicresin film 8109 and the portion of the first inorganic insulating film8108 that is exposed in the opening. The second inorganic insulatingfilm 8110 is, similar to the first inorganic insulating film 8108, aninsulating film containing nitrogen and transmits less moisture than anorganic resin film which is formed later does.

The first inorganic insulating film 8108 and the second inorganicinsulating film 8110 are used as dielectric of capacitors. Therefore, ifthe first and second inorganic insulating films are too thick, thecapacitance value of the capacitors is reduced and treatment time forforming the films is prolonged. On the other hand, too thin first andsecond inorganic insulating films have only a small degree of effect inpreventing permeation of moisture. In the bottom gate TFT, the gateinsulating film 8103 is also between the first capacitor electrode 8107and a second capacitor electrode 8112 and is used as a part of thedielectric. Therefore, it is necessary to determine the thicknesses ofthe first inorganic insulating film 8108 and the second inorganicinsulating film 8110, taking into account the thickness of the gateinsulating film 8103. Preferably, the first inorganic insulating film8108 and the second inorganic insulating film 8110 each have a thicknessof about 10 to 200 nm, and the total thickness of the three layers,namely, the first and second inorganic insulating films plus the gateinsulating film, is preferably about 30 to 500 nm.

A contact hole is formed by dry etching through the gate insulating film8103, the first inorganic insulating film 8108, and the second inorganicinsulating film 8110 so that a part of the semiconductor film is exposedin the opening of the organic resin film 8109. During the dry etching,the semiconductor film 8102 serves as an etching stopper.

The first inorganic insulating film 8108 and the second inorganicinsulating film 8110 existing above the first capacitor electrode 8107are kept covered with a resist mask during the dry etching in order toavoid being etched.

The resist mask is then removed using a developer. A developer ingeneral is an alkaline aqueous solution and contains a large amount ofmoisture. In the present invention, the organic resin film 8109 iscovered with the first inorganic insulating film 8108 and the secondinorganic insulating film 8110 to avoid direct exposure to a developer.Therefore, moisture in the developer is mostly prevented from enteringthe organic resin film 8109 and hardly causes swelling. Accordingly,heat treatment for removal of moisture after the resist mask is removedusing the developer can be finished in a shortened period of time.

Then a conductive film is formed on the second inorganic insulating film8110 so as to cover the contact hole. The conductive film is etched toform a wiring 8111 which is connected to the semiconductor film 8102,and the second capacitor electrode 8112. The second capacitor electrode8112 overlaps the first capacitor electrode 8107 sandwiching between thefirst inorganic insulating film 8108 and the second inorganic insulatingfilm 8110. The second capacitor electrode 8112, the first inorganicinsulating film 8108, the second inorganic insulating film 8110, and thefirst capacitor electrode 8107 form capacitor storage 8113.

The description given next is about the structure of a protectivecircuit of a semiconductor display device of the present invention. FIG.6 is a top view of an element substrate of a semiconductor displaydevice of the present invention on which a semiconductor element isformed.

The element substrate is obtained by forming, on a substrate 4001, apixel portion 4002, a signal line driving circuit 4003, a first scanningline driving circuit 4004 a, and a second scanning line driving circuit4004 b. In the present invention, the number of signal line drivingcircuits and the number of scanning line driving circuits are notlimited to those in FIG. 6. How many signal line driving circuits andscanning line driving circuits are to be provided can be set at adesigner's discretion.

Denoted by 4005 is a lead wiring for supplying power supply voltage orvarious signals to the pixel portion 4002 and the first and secondscanning line driving circuits 4004 a and 4004 b.

A signal inputted to an input terminal 4006 is supplied to the leadwiring 4005 after its noise is removed by a protective circuit 4009. Theprotective circuit 4009 also prevents static electricity discharged fromthe input terminal 4006 from being sent to downstream circuits.

FIG. 7 is an equivalent circuit diagram of the protective circuit 4009.The protective circuit shown in FIG. 7 is merely an example of theprotective circuit of the semiconductor display device of the presentinvention, and the present invention is not limited to this structure.

The protective circuit shown in FIG. 7 is for one input terminal, andhas two p-channel TFTs 4010 and 4011, two capacitor storage 4012 and4013, and a resistor 4014. Although p-channel TFTs are used in FIG. 7,n-channel TFTs may be employed instead. The two p-channel TFTs 4010 and4011 may be multi-channel TFTs in which a channel formation region isdivided into two or more regions.

A gate of the p-channel TFT 4010 receives a power supply voltage Vdd.One of its two impurity regions receives the power supply voltage Vddwhereas the other receives a voltage Vin from the input terminal.

In this specification, voltage means an electric potential differencefrom a ground voltage Gnd unless otherwise stated.

A gate of the other p-channel TFT, i.e., the TFT 4011, receives thevoltage Vin from the input terminal. One of its two impurity regionsreceives the ground voltage Gnd whereas the other receives the voltageVin from the input terminal.

The capacitor storage 4012 has two electrodes (a first capacitorelectrode and a second capacitor electrode) and one of them receives thevoltage Vin from the input terminal whereas the other receives the powersupply voltage Vdd. The capacitor storage 4013 has two electrodes (afirst capacitor electrode and a second capacitor electrode) and one ofthem receives the voltage Vin from the input terminal whereas the otherreceives the ground voltage Gnd.

The resistor 4014 has two terminals and one of the terminals receivesthe voltage Vin from the input terminal whereas the other terminalreceives the ground voltage Gnd. The resistor 4014 is provided to makethe voltage of the lead wiring drop to Gnd when the input terminal stopsreceiving the voltage Vin, and its resistance has to be set sufficientlylarger than the wiring resistance of the lead wiring.

Next, the operation of the protective circuit shown in FIG. 7 will bedescribed. The description here takes as an example a case in which avoltage of a clock signal at a certain frequency is inputted as theinput voltage Vin to the input terminal. The voltage of the clock signaloscillates between the voltage Vdd and the voltage Gnd.

FIG. 9A is a timing chart of the input voltage Vin when the clock signalcontains noise. The input voltage Vin temporarily rises higher than Vddor drops lower than Gnd upon the moment of its rise and fall.

When the input voltage Vin rises higher than the voltage Vdd, thevoltage Vdd applied to the gate and one of the impurity regions of thep-channel TFT 4010 shown in FIG. 7 becomes lower than the voltage Vinapplied to the other impurity region. This turns the p-channel TFT 4010on. The p-channel TFT 4011 remains turned off since the voltage Vinapplied to its gate and one of the impurity regions is sufficientlyhigher than the voltage Gnd applied to the other impurity region.

FIG. 8A gives a brief illustration on connection in the protectivecircuit when the input voltage Vin becomes higher than the voltage Vdd.In FIG. 8A, the p-channel TFTs 4010 and 4011 are shown simply asswitches. When the p-channel TFT 4010 is turned on whereas the p-channelTFT 4011 is turned off, the power supply voltage Vdd is given to thelead wiring through the p-channel TFT 4010. Accordingly, the voltagegiven to the lead wiring does not exceed Vdd even when noise raises thevoltage from the input terminal above Vdd.

When the input voltage Vin becomes lower than the voltage Gnd, on theother hand, the voltage Vdd applied to the gate and one of the impurityregions of the p-channel TFT 4010 shown in FIG. 7 is sufficiently higherthan the voltage Vin applied to the other impurity region. This turnsthe p-channel TFT 4010 off. On the other hand, the p-channel TFT 4011 isturned on since the voltage Vin applied to its gate and one of theimpurity regions becomes lower than the voltage Gnd applied to the otherimpurity region.

FIG. 8B gives a brief illustration on connection in the protectivecircuit when the input voltage Vin becomes lower than the voltage Gnd.In FIG. 8B, the p-channel TFTs 4010 and 4011 are shown simply asswitches. When the p-channel TFT 4010 is turned off whereas thep-channel TFT 4011 is turned on, the power supply voltage Gnd is givento the lead wiring through the p-channel TFT 4011. Accordingly, thevoltage given to the lead wiring does not become lower than Gnd evenwhen noise lowers the voltage from the input terminal below Gnd.

Furthermore, the capacitor storage 4012 and 4013 can dull the pulse-likenoise down to the voltage from the input terminal and can avoid to acertain degree a rapid change in voltage due to noise.

Therefore, the voltage of the lead wiring is kept within a range betweenthe voltage Gnd and the power supply voltage Vdd as shown in FIG. 9B,and the wiring is protected against application of extraordinary high orlow voltage outside this range.

With the protective circuit provided in the input terminal to which asignal is inputted, when no signal is putted, the voltage of every leadwiring to which a signal is given is kept at a fixed level (here, Gnd).In other words, the protective circuit has the function of a shortcircuit ring which can bring wirings to the short circuit state when nosignal is inputted. Electrostatic discharge damage due to voltagedifference between lead wirings is thus prevented. When a signal isinputted, the resistance of the resistor 4014 is sufficiently large andtherefore the voltage of a signal given to the lead wiring is not pulleddown by the ground voltage.

In the protective circuit shown in FIG. 7, the larger the ON current ofthe p-channel TFTs 4010 and 4011 is, the quicker the voltage of the leadwiring is set and kept to the power supply voltage Vdd when the inputvoltage Vin exceeds the power supply voltage Vdd. On the other hand,when the input voltage Vin becomes lower than the voltage Gnd, thevoltage of the lead wiring is set and kept to the voltage Gnd quickly.

FIG. 10 shows an example in which the p-channel TFTs 4010 and 4011 ofthe protective circuit of FIG. 7 are each substituted by two double-gateTFTs. The protective circuit shown in FIG. 10 has double-gate p-channel.TFTs 4100 to 4103, capacitor storage 4104 and 4105, and a resistor 4106.

In a double-gate, triple-gate, or other multi-gate TFT, two, three, ormore channel formation regions are formed in one active layer, and everychannel formation region is interposed between an impurity regionfunctioning as source and an impurity region functioning as drain. Suchmulti-gate TFT can be substituted by serially-connected TFTs in whichone or more channel formation regions are formed in one active layer andgates are connected to one another.

In the p-channel TFTs 4100 and 4101, the power supply voltage Vdd isgiven to a gate and one of impurity regions, and the input voltage Vinis given to the other impurity region. In the p-channel TFTs 4102 and4103, the input voltage Vin is given to a gate and one of impurityregions and the voltage Gnd is given to the other impurity region.

The capacitor storage 4104 has two electrodes (a first capacitorelectrode and a second capacitor electrode), and one of them receivesthe voltage Vin from the input terminal whereas the other receives thepower supply voltage Vdd. The capacitor storage 4105 has two electrodes(a first capacitor electrode and a second capacitor electrode), and oneof them receives the voltage Vin from the input terminal whereas theother receives the ground voltage Gnd.

The resistor 4106 has two terminals, and one of the terminals receivesthe voltage Vin from the input terminal whereas the other terminalreceives the ground voltage Gnd. The resistor 4106 is provided to makethe voltage of the lead wiring drop to Gnd when the input terminal stopsreceiving the voltage Vin, and its resistance has to be set sufficientlylarger than the wiring resistance of the lead wiring.

In the protective circuit shown in FIG. 7 or 10, a power supply voltageVss, which is not equal to the ground voltage and lower than the voltageVdd, may be used instead of the ground voltage Gnd.

FIG. 11 shows an example of a top view of the protective circuit shownin FIG. 10. A sectional view taken along the line A-A′ in FIG. 11corresponds to FIG. 12. A semiconductor film 4220 is formed on a basefilm 4208 which is composed of an insulating film. The semiconductorfilm 4220 has impurity regions 4225 to 4229 and channel formationregions 4221 to 4224 between the impurity regions. A gate insulatingfilm 4209 covers the semiconductor film 4220.

Gate electrodes 4202 to 4205 are formed above the channel formationregions 4221 to 4224 so that the gate insulating film 4209 is sandwichedbetween the channel formation regions and the gate electrodes. A firstcapacitor electrode 4206 is formed on the gate insulating film 4209 fromthe same conductive film that is used to form the gate electrodes 4202to 4205.

The gate electrodes 4202 to 4205 are all electrically connected. Thesemiconductor film 4220, the gate insulating film 4209, and the gateelectrodes 4202 to 4205 constitute the TFTs 4102 and 4103.

Then a first inorganic insulating film 4210 is formed so as to cover theTFTs 4102 and 4103 and the first capacitor electrode 4206. An organicresin film 4211 with openings is formed covering the first inorganicinsulating film 4210. The organic resin film 4211 is a photosensitivepositive acrylic film and the opening is formed by exposure to light andsubsequent development. The first inorganic insulating film 4210 isexposed in the openings of the organic resin film 4211.

Then a second inorganic insulating film 4212 is formed on the organicresin film 4211 covering the openings. RF sputtering is used to form thesecond inorganic insulating film 4212.

The gate insulating film 4209, the first inorganic insulating film 4210,and the second inorganic insulating film 4212 are etched by dry etchingto form contact holes in the openings of the organic resin film 4211.The impurity regions 4225, 4227, and 4229 are partially exposed in thecontact holes. In the dry etching, measures have to be taken to avoidetching portions of the first inorganic insulating film 4210 and thesecond inorganic insulating film 4212 that are above the first capacitorelectrode 4206. Also, the organic resin film 4211 must not be exposed inthe openings.

A conductive film is formed on the second inorganic insulating film 4212to cover the contact holes and is patterned to form a wiring 4200 and awiring 4201. The wiring 4200 is connected to the impurity regions 4225and 4229 that function as source or drain. The wiring 4201 is connectedto the impurity region 4227 that functions as source or drain.

A part of the wiring 4200 functions as a second capacitor electrode andoverlaps the first capacitor electrode 4206 in the opening of theorganic resin film 4211 with the first inorganic insulating film 4210and the second inorganic insulating film 4212 sandwiched between thecapacitor electrodes.

In the present invention, the surface of the organic resin film isprevented from being roughened through dry etching by covering theorganic resin film with an inorganic insulating film. The pixelelectrode or the like that is formed later is therefore saved fromsurface irregularities and uneven thickness, thereby preventing unevendisplay.

Covering the organic resin film with a nitrogen-containing inorganicinsulating film that transmits less moisture than the organic resin filmdoes also prevents the organic resin film from releasing its moisturewhereas it prevents the organic resin film from absorbing moisture andswelling. Corrosion of the wirings by moisture released from the organicresin film is therefore avoided. In the case of a light emitting devicethat uses a light emitting element represented by an organic lightemitting diode (OLED), it also prevents moisture released from theorganic resin film from degrading the luminance of the light emittingelement.

Moreover, by covering the entire organic resin film with an inorganicinsulating film so that none of the organic resin film is exposed, theorganic resin film is prevented from swelling with water in an alkalineaqueous solution which is used in development and heat treatment forremoval of moisture after the development can be finished in a shortenedperiod of time. This is more effective in preventing the organic resinfilm from releasing its moisture into adjacent films or electrodes.Therefore, the long-term reliability of the panel can be enhanced.

When non-photosensitive organic resin is employed, commonly dry etchingis used to form an opening in an interlayer insulating film. Dry etchingis an etching method that uses plasma of active radical or reactive gas.The interlayer insulating film is ten times as thick as a gateinsulating film, and dry etching to form an opening therein takes time.If a substrate on which a TFT is formed is exposed to plasma for a longperiod of time, the TFT threshold is easily fluctuated toward the plusside because of so-called charging damage in which holes are trapped ina gate insulating film. By employing photosensitive organic resin andusing wet etching to form an opening as in the present invention, thedry etching period is significantly shortened and fluctuation of TFTthreshold is therefore prevented.

The capacitor of the protective circuit which protects the semiconductorelement against degradation or breakage brought by static electricitydischarge and which prevents malfunction of a semiconductor element dueto noise is composed of the above capacitor storage. The above structuremakes it easy to form the protective circuit on the same substrate wherethe pixel portion is formed and prevents degradation or breakage of asemiconductor element due to static electricity as well as malfunctionby noise to avoid image disturbance.

The surface of the organic resin film is prevented from being roughenedthrough dry etching by covering the organic resin film with an inorganicinsulating film. Surface irregularities of a pixel electrode or othercomponents formed later are thus avoided as well as uneven thickness ofthe pixel electrode, making it possible to prevent uneven display.

Covering the organic resin film with a nitrogen-containing inorganicinsulating film that transmits less moisture than the organic resin filmdoes also prevents the organic resin film from releasing its moisturewhereas it prevents the organic resin film from absorbing moisture andswelling. Corrosion of the wirings by moisture released from the organicresin film is therefore avoided. In the case of a light emitting devicethat uses a light emitting element represented by an organic lightemitting diode (OLED), it also prevents moisture, which is released fromthe organic resin, film from degrading the luminance of the lightemitting element.

Moreover, by covering the entire organic resin film with an inorganicinsulating film so that none of the organic resin film is exposed, theorganic resin film is prevented from swelling with water in an alkalineaqueous solution which is used in development and the heat treatmenttime for removal of moisture after the development can be shortened.This is more effective in preventing the organic resin film fromreleasing its moisture into adjacent films or electrodes and thereforethe long-term reliability of the panel can be enhanced.

When non-photosensitive organic resin is employed, commonly dry etchingis used to form an opening in the interlayer insulating film. Dryetching is an etching method that uses plasma of active radical orreactive gas. The interlayer insulating film is ten times as thick as agate insulating film and dry etching to form an opening therein takestime. If a substrate on which a TFT is formed is exposed to plasma for along period of time, the TFT threshold is easily fluctuated toward theplus side because of so-called charging damage in which holes aretrapped in a gate insulating film. By employing photosensitive organicresin and using wet etching to form an opening as in the presentinvention, the dry etching period is significantly shortened andfluctuation of TFT threshold is therefore prevented.

The capacitor of the protective circuit which protects the semiconductorelement against degradation or breakage brought by static electricitydischarge and which prevents malfunction of a semiconductor element dueto noise, is composed of the above capacitor storage. This makes it easyto form the protective circuit on the same substrate where the pixelportion is formed and prevents degradation or breakage of asemiconductor element due to static electricity as well as malfunctionby noise.

As described above, research by the applicant of the present inventionshows a fact that, when a resin film is used as an interlayer insulatingfilm and a contact hole is formed using dry etching, thin filmtransistors obtained are largely fluctuated in threshold voltage (Vth).For instance, the data shown in FIG. 29 are results of investigation onfluctuation in threshold voltage among thin film transistors formed onan SOI substrate. Black circular marks in the graph express in a casewhere the interlayer insulating film has a laminate structure consistingof a silicon nitride (SiN) film and an acrylic film. White triangularmarks in the graph express in a case where the interlayer insulatingfilm has a laminate structure consisting of a silicon nitroxide (SiNO)film and a silicon oxynitride (SiON) film. The contact hole is openedusing dry etching in either case. The difference between SiNO and SiONused herein is that nitrogen atomic % is larger than oxygen atomic % inthe former whereas oxygen atomic % is larger than nitrogen atomic % inthe latter.

The data in FIG. 29 are made into a graph through estimation bystatistical work of threshold voltage fluctuation, in which thehorizontal axis shows the channel length (how far carriers move) and thevertical axis shows the Vth fluctuation. In recent years, statisticalwork called ‘quartile deviation’ becomes widely recognized. Quartiledeviation shows the difference between the 25% value and the 75% valuein normal probability graph and is noticed as statistical work that isnot influenced by peculiar values. Based on quartile deviation, theapplicants of the present invention have defined the difference betweenthe 16% value and the 84% value as 16% quantile deviation and plotted itinto the vertical axis as ‘Vth fluctuation’. The 16% quantile deviationcorresponds to ±σ in normal probability distribution and therefore dataplot used is obtained by multiplying each by a coefficient to make theminto values deemed as ±3σ. According to the data, the fluctuation isabout 4 times (in n-channel TFTs) or twice (in p-channel TFTs) largerwhen an acrylic film is used as the interlayer insulating film. It isobviously that the use of the acrylic film increases the fluctuation.The applicants of the present invention infer that the threshold voltagefluctuation is caused by electric charges trapped in the acrylic filmdue to plasma damage received during dry etching.

EMBODIMENTS

Embodiments of the present invention will be described below.

Embodiment 1

In this embodiment, a manufacturing method of a light emitting devicewhich is one of the semiconductor display devices of the presentinvention will be described. Note that, in this embodiment, a method ofmanufacturing a pixel portion and a storage capacitor included in aprotective circuit at the same time will be described in detail.

First, as shown in FIG. 13A, a base film 5002 including an insulatingfilm such as a silicon oxide film, a silicon nitride film, or a siliconoxynitride film is formed on a substrate 5001 including glass such asbarium borosilicate glass or aluminoborosilicate glass represented by#7059 glass, #1737 glass, and the like of Corning Corporation. Forexample, a silicon oxynitride film 5002 a manufactured from SiH₄, NH₃,and N₂O is formed with a thickness of 10 to 200 nm (preferably 50 to 100nm) by the plasma CVD method, and a silicon oxynitride hydrogenate film5002 b manufactured from SiH₄ and N₂O is likewise formed with athickness of 50 to 200 nm (preferably 100 to 150 nm) in a laminatedshape. Although the base film 5002 is shown as having a two layerstructure in this embodiment, it may be formed as a single layer film ofthe insulating film or a structure in which the insulating film islaminated in two or more layers.

Island-shaped semiconductor layers 5003 and 5004 are formed of acrystalline semiconductor film which is manufactured by crystallizing asemiconductor film having an amorphous structure with the lasercrystallization method or a publicly known thermal crystallizationmethod. These island-shaped semiconductor layers 5003 and 5004 areformed with a thickness of 25 to 80 nm (preferably 30 to 60 nm). Amaterial of the crystalline semiconductor film is not limited but ispreferably formed of silicon, silicon germanium (SiGe), or the like.

In order to manufacture the. crystalline semiconductor film with thelaser crystallization method, an excimer laser, a YAG laser, or a YVO₄laser of a pulse oscillation type or a continuous light emitting type isused. In the case of using these lasers, it is favorable to use a methodof condensing laser beams, which are radiated from a laser oscillator ina linear shape by using an optical system, and then irradiating them ona semiconductor film. Although conditions of crystallization areappropriately selected by an operator in the case of using the excimerlaser, it is favorable to set a pulse oscillation frequency to 300 Hzand a laser energy density to 100 to 400 mJ/cm² (representatively, 200to 300 mJ/cm²). In addition, in the case of using the YAG laser, it isfavorable to use a second higher harmonic and set the pulse oscillationfrequency to 30 to 300 kHz and the laser energy density to 300 to 600mJ/cm² (representatively, 350 to 500 mJ/cm²). Then, the laser beamscondensed in a linear shape are irradiated over an entire surface of asubstrate with a width of 100 to 1000 μm, for example, 400 μm. At thispoint, an overlap ratio of the linear laser beams is set to 50 to 90%.

Note, that not only silicon but also silicon germanium may be used inthe semiconductor film. In the case of using the silicon germanium, aconcentration of the germanium is preferably about 0.01 to 4.5 atomic %.

Subsequently, a gate insulating film 5007 covering the island-shapedsemiconductor layers 5003 and 5004 is formed. The gate insulating film5007 is formed of an insulating film containing silicon with a thicknessof 40 to 150 nm using the plasma CVD method or the sputtering method. Inthis embodiment, the gate insulating film 5007 is formed of a siliconoxynitride film with a thickness of 120 nm. It is needless to mentionthat the gate insulating film is not limited to such a siliconoxynitride film and other insulating film containing silicon may be usedin a single layer or a laminated layer structure. For example, in thecase of using a silicon oxide film, the silicon oxide film is formed bymixing TEOS (Tetraethyl Orthosilicate) and O₂ with the plasma CVDmethod, setting a reactive pressure and a substrate temperature thereofto 40 Pa and 300 to 400° C., respectively, and discharging the mixedTEOS and O₂ at a high frequency (13.56 MHz), a power flux density of 0.5to 0.8 W/cm². The silicon oxide film manufactured in this way canthereafter obtain favorable characteristics as a gate insulating filmthrough thermal annealing at 400 to 500° C. In addition, aluminumnitride can be used as a gate insulting film. Since the aluminum nitridehas relatively high thermal conductivity, heat generated by a TFT can bediffused efficiently. Further, after forming silicon oxide, siliconoxynitride, or the like which does not contain aluminum, a filmlaminated aluminum nitride thereon may be used as a gate insulatingfilm.

Then, a first conductive film 5008 and a second conductive film 5009 forforming a gate electrode on the gate insulating film 5007 are formed. Inthis embodiment, the first conductive film 5008 is formed of Ta with athickness of 50 to 100 nm and the second conductive film 5009 is formedof W with a thickness of 100 to 300 nm.

A Ta film is formed by sputtering a target of Ta with Ar. In this case,if an appropriate amount of Xe or Kr is added to Ar, an internal stressof the Ta film can be eased to prevent exfoliation of the film. Inaddition, a Ta film of a α phase has a resistivity of approximately 20μΩcm and can be used for a gate electrode, but a Ta film of a β phasehas a resistivity of approximately 180 μΩcm and is not suitable to useas a gate electrode. In order to form the Ta film of the α phase, iftantalum nitride having a crystal structure close to the α phase of Tais formed as a base of Ta with a thickness of approximately 10 to 50 nm,the Ta film of the α phase can be obtained easily.

When a W film is formed, it is formed by the sputtering method targetingW. Besides, the W film can also be formed by thermal CVD method usingtungsten hexafluoride (WF₆). In any case, it is necessary to realize alow resistivity in order to use the W film as a gate electrode, and itis desirable to set a resistivity of the W film to 20 μΩcm or less.Reduction of a resistivity can be realized in the W film by increasing asize of a crystal grain. However, when a large quantity of impuritycomponents such as oxygen is contained in W, crystallization is hinderedand a resistivity of the W film is increased. Consequently, when the Wfilm is formed by the sputtering method, the W film is formed using a Wtarget with a purity of 99.99 or 99.9999% and giving carefulconsideration such that impurities are not mixed from a chemical vaporat the time of film formation, whereby a resistivity of 9 to 20 μΩcm canbe realized.

Note that, although the first conductive film 5008 is assumed to be Taand the second conductive film 5009 is assumed to be W in thisembodiment, both the conductive films are not specifically limited butmay be formed of an element selected out of Ta, W, Ti, Mo, Al, and Cu,or an alloy material or a compound material containing the element as amain component. In addition, a semiconductor film represented by apolysilicon film doped with an impurity element such as phosphorus maybe used. As examples of a combination other than this embodiment, acombination of the first conductive film formed of tantalum nitride(TaN) and the second conductive film formed of W, a combination of thefirst conductive film formed of tantalum nitride (TaN) and the secondconductive film formed of Al, and a combination of the first conductivefilm formed of tantalum nitride. (TaN) and the second conductive filmformed of Cu are preferable. In addition, a semiconductor filmrepresented by a polysilicon film doped with an impurity element such asphosphorus or an AgPdCu alloy may be used as the first conductive filmand the second conductive film.

In addition, the gate electrode is not limited to the two-layerstructure but may be a three-layer structure of, for example, a tungstenfilm, a film of an alloy of aluminum and silicon (Al—Si), and a titaniumnitride film laminated one after another. Further, when the gateelectrode is formed in the three-layer structure, tungsten nitride maybe used instead of tungsten, a film of an alloy of aluminum and titanium(Al—Ti) may be used instead of the film of the alloy of aluminum andsilicon (Al—Si), and a titanium film may be used instead of the titaniumnitride film.

Note that it is important to appropriately select an optimum etchingmethod or a type of an etchant depending upon materials of conductivefilms.

Next, a mask 5010 with resist is formed, and first etching treatment isperformed in order to form an electrode and a wiring. In thisembodiment, the first etching treatment is performed by using an ICP(Inductively Coupled Plasma) etching method, mixing CF₄ and Cl₂ in a gasfor etching, and inputting an RF (13.56 MHz) power of 500 W in anelectrode of a coil type at a pressure of 1 Pa to generate plasma. An RF(13.56 MHz) power of 100 W is also inputted on the substrate side(sample stage), and a substantially negative self-bias voltage isapplied thereto. When CF₄ and Cl₂ are mixed, both of the W film and theTa film are etched to the same degree.

With the above-mentioned etching conditions, ends of the firstconductive film and the second conductive film are formed in a tapershape according to an effect of the bias voltage applied to thesubstrate side by making a shape of the mask with resist suitable. Anangle of the taper portion becomes 15 to 45°. In order to etch a gateinsulating without leaving a residuum on the gate insulating film, it isfavorable to increase etching time at a rate of approximately 10 to 20%.Since a selection ratio of a silicon oxynitride film with respect to theW film is 2 to 4 (representatively, 3), a surface where the siliconoxynitride film is exposed is etched by approximately 20 to 50 nm byover etching treatment. In this way, conductive layers of a first shape5011 to 5014 (first conductive layers 5011 a to 5014 a and secondconductive layers 5011 b to 5014 b) consisting of the first conductivelayer and the second conductive layer are formed by the first etchingtreatment. At this point, in the gate insulating film 5007, a region notcovered by the conductive layers of the first shape 5011 to 5014 isetched by approximately 20 to 50 nm, and a thinned region is formed(FIG. 13B).

Then, first doping treatment is performed to add an impurity element forgiving an N type is added (FIG. 13C). A method of doping may be an iondope method or an ion implantation method. As conditions of the ion dopemethod, a doze quantity is set to 1×10¹³ to 5×10¹⁴ atoms/cm², and anacceleration voltage is set to 60 to 100 keV. As the impurity elementgiving the N type, an element belonging to the XV group, typically,phosphorus (P) or arsenic (As) is used. In this embodiment, phosphorus(P) is used. In this case, the conductive layers 5011 to 5013 becomes amask against the impurity element giving the N type, and first impurityregions 5017 to 5021 are formed in a self-aligning manner. The impurityelement giving the N type is added to the first impurity regions 5017 to5021 in a concentration range of 1×10²⁰ to 1×10²¹ atoms/cm³.

Next, second etching treatment is performed as shown in FIG. 14A.Similarly, the second etching treatment is performed by using the ICP(Inductively Coupled Plasma) etching method, mixing CF₄, Cl₂ and O₂ inan etching gas, and inputting a RF (13.56 MHz) power of 500 W in anelectrode of a coil type at a pressure of 1 Pa to generate plasma. A RF(13.56 MHz) power of 50 W is inputted on the substrate side (samplestage), and a self-bias voltage lower than that in the first etchingtreatment is applied thereto. The W film is subjected to the anisotropicetching under such conditions and Ta which is the first conductive filmis subjected to the anisotropic etching at an etching speed, which isslower than that for etching the W film, to form conductive layers of asecond shape 5026 to 5029 (first conductive layers 5026 a to 5029 a andsecond conductive layers 5026 b to 5029 b). At this point, in the gateinsulating film 5007, a region not covered by the conductive layers ofthe second shape 5026 to 5029 are further etched by approximately 20 to50 nm and a thinned region is formed.

An etching reaction of the W film and the Ta film due to the mixed gasof CF₄ and Cl₂ can be surmised from a radical or an ion type to begenerated and a vapor pressure of a reaction product. Comparing vaporpressures of fluorides and chlorides of W and Ta are compared, WF₆ whichis a fluoride of W has an extremely high vapor pressure and the otherfluorides and chlorides WCl₅, TaF₅, and TaCl₅ have similar vaporpressures of the same degree. Therefore, both of the W film and the Tafilm are etched with the mixed gas of CF₄ and Cl₂. However, when anappropriate quantity of O₂ is added to this mixed gas, CF₄ and O₂ reactwith each other to change to CO and F, and a large quantity of an Fradical or an F ion is generated. As a result, an etching speed of the Wfilm having a high vapor pressure of a fluoride increases. On the otherhand, Ta has relatively little increase in an etching speed even if Fincreases. In addition, since Ta is more likely to be oxidized comparedwith W, a surface of Ta is oxidized by adding O₂. Since an oxide of Tadoes not react with fluorine or chlorine, the etching speed of the Tafilm further decreases. Therefore, it becomes possible to differentiateetching speeds of the W film and the Ta film, and to make the etchingspeed of the W film higher than that of the Ta film.

Then, as shown in FIG. 14B, second doping treatment is performed. Inthis case, an impurity element giving the N type is doped withconditions that a doze quantity is decreased to be lower than that inthe first doping treatment and an acceleration is increased to be higherthan that in the first doping treatment. For example, the second dopingtreatment is performed with the acceleration voltage of 70 to 120 keVand the doze quantity of 1×10¹³ atoms/cm² to form a new impurity regionon the inner side of the first impurity regions which are formed in theisland-shaped semiconductor layer in FIG. 13C. The doping is performedsuch that the impurity element is also added to a region on the lowerside of the second conductive layers 5026 a to 5028 a using theconductive layers of the second shape 5026 and 5028 as a mask againstthe impurity element. In this way, third impurity regions 5032 to 5037overlapping the second conductive layers 5026 a to 5028 a and secondimpurity regions 5042 to 5047 between the first impurity regions and thethird impurity regions are formed. The impurity element giving the Ntype is adapted to have a concentration of 1×10¹⁷ to 1×10¹⁹ atoms/cm³ inthe second impurity regions and 1×10¹⁶ to 1×10¹⁸ atoms/cm³ in the thirdimpurity regions.

Then, as shown in FIG. 14C, fourth impurity regions 5052 to 5057 of anopposite conductive type of the first conductive type are formed in theisland-shaped semiconductor layer 5004 forming the p-channel TFT. Theimpurity regions are formed in a self-aligning manner using the secondconductive layer 5028 b as a mask against an impurity element. At thispoint, the island-shaped semiconductor layer 5003 and the firstcapacitor electrode 5029 forming the n-channel TFT are coated entirelywith a resist mask 5200. Although phosphorus is added at differentconcentrations in the respective impurity regions 5052 to 5057, theimpurity regions are formed by an ion dope method using diborane (B₂H₆)and are adapted to have an impurity concentration of 2×10²⁰ to 2×10²¹atoms/cm³ in any region.

The impurity regions are formed in the respective island-shapedsemiconductor layers in the above-mentioned process. The secondconductive layers 5026 to 5028 overlapping the island-shapedsemiconductor layers function as the gate electrode. In addition, thesecond conductive layer 5029 functions as the first electrode forcapacitor.

Then, with an object of conductive type control, a process foractivating the impurity elements added to the respective island-shapedsemiconductor layer is performed. This process is performed by a thermalanneal method using an anneal furnace. Besides, a laser anneal method ora rapid thermal anneal method (RTA method) can be applied. In thethermal anneal method, the process is performed in a nitrogen atmospherewith an oxygen concentration of 1 ppm or less, preferably 0.1 ppm orless, at a temperature of 400 to 700° C., representatively, 500 to 600°C. In this embodiment, heat treatment is performed at 500° C. for fourhours. However, when the wiring material used in the second conductivelayers 5026 to 5029 is susceptible to heat, it is preferable to form aninterlayer insulating film (containing silicon as a main component) inorder to protect the wiring and the like, and then activate the film.

Moreover, a process for performing heat treatment at a temperature of300 to 450° C., for 1 to 12 hours in an atmosphere containing 3 to 100%of hydrogen to hydrogenate the island-shaped semiconductor layer isperformed. This process is a process for terminating dangling bond of asemiconductor layer with thermally excited hydrogen. As other means ofhydrogenation, plasma hydrogenation (using hydrogen excited by plasma)may be performed.

Subsequently, as shown in FIG. 15A, a first inorganic insulating film5060 consisting of silicon oxynitride with a thickness of 10 to 200 nmis formed using the CVD method. Note that the first inorganic insulatingfilm is not limited to a silicon oxynitride film, and any inorganicinsulating film containing nitrogen may be used as the first inorganicinsulating film as long as the film can suppress penetration of moistureshifting from an organic resin film which is formed later. For example,silicon nitride, aluminum nitride, or aluminum oxynitride can be used.

Note that aluminum nitride has a relatively high thermal conductivityand can effectively diffuse heat generated in a TFT or a light emittingelement.

Next, an organic resin film 5061 consisting of a positive photosensitiveorganic resin is formed on the first inorganic insulating film 5060.Although the organic resin film 5061 is formed using positivephotosensitive acrylic in this embodiment, the present invention is notlimited to this.

In this embodiment, the organic resin film 5061 is formed by applyingpositive photosensitive acrylic with a spin coat method and baking thesame. Note that a film thickness of the organic resin film 5061 is setto be approximately 0.7 to 5 μm (preferably, 2 to 4 μm) after baking.

Next, a part where an opening is to be formed is exposed to light usinga photo mask. Then, after developing with a developer containing TMAH(tetramethyl ammonium hydroxide) as a main component, the substrate isdried, and baking is performed at 220° C. for one hour approximately.Then, as shown in FIG. 15B, the opening is formed in the organic resinfilm 5061, and a part of the first inorganic insulating film 5060 isexposed in the opening.

Note that, since the positive photosensitive acrylic is colored lightbrown, it is subjected to decolorizing treatment when light emitted froma light emitting element travels to the substrate side. In this case,before baking, the entire photosensitive acrylic after development isexposed to light again. In the exposure at this point, slightly strongerlight is irradiate compared with the exposure for forming the opening orirradiation time is extended such that the exposure can be performedcompletely. For example, when a positive acrylic resin with a filmthickness of 2 μm is decolorized, in case of a nonmagnificationprojection aligner (more specifically, MPA manufactured by Canon Inc.)utilizing multi-wavelength light consisting of a g ray (436 nm), an hray (405 nm), and an i ray (365 nm) which are spectrum light of anultrahigh pressure mercury vapor lamp is used, the light is irradiatedfor approximately 60 sec. The positive acrylic resin is completelydecolorized by this exposure.

In addition, although baking is performed at the temperature of 220° C.after development in this embodiment, baking may be performed at a hightemperature of 220° C. after performing baking at a low temperature of100° C. as pre-baling after development.

Then, as shown in FIG. 15C, covering the opening in which a part of thefirst inorganic insulating film 5060 is exposed and the organic resinfilm 5061, a second inorganic insulating film 5062 consisting of siliconnitride is formed using an RF sputtering method. A film thickness of thesecond inorganic insulating film 5062 is desirable to be approximately10 to 200 nm. In addition, the second inorganic insulating film is notlimited to a silicon oxynitride film, and any inorganic insulating filmcontaining nitrogen may be used as the second inorganic insulating filmas long as the film can suppress penetration of moisture shifting fromthe organic resin film 5061. For example, silicon nitride, aluminumnitride, or aluminum oxynitride can be used.

Note that in a silicon oxynitride film or an aluminum oxynitride film, aratio of atomic % of oxygen and nitrogen thereof greatly relates to abarrier property of the same. The higher the ratio of nitrogen to oxygenis, the higher the barrier property is. In addition, more specifically,a ratio of nitrogen is desirable to be higher than a ratio of oxygen.

In addition, a film formed using the RF sputtering method is high indenseness and excellent in the barrier property. As conditions of the RFsputtering, for example, when a silicon oxynitride film is formed, witha Si target, gases of N₂, Ar, and N₂O are flown such that a flow ratiothereof becomes 31:5:4, and the film is formed with a pressure of 0.4 Paand an electric power of 3000 W. In addition, for example, when asilicon nitride film is formed, with a Si target, gases of N₂ and Ar areflown such that a flow ratio in a chamber becomes 20:20, and the film isformed with a pressure of 0.8 Pa, an electric power of 3000 W, and afilm formation temperature of 215° C.

A first interlayer insulating film is formed of this organic resin film5061, the first inorganic insulating film 5060, and the second inorganicinsulating film.

Next, as shown in FIG. 16A, in the opening of the organic resin film5061, a contact hole is formed in the gate insulating film 5007, thefirst inorganic insulating film 5060, and the second inorganicinsulating film 5062 using the dry etching method.

By the opening of this contact hole, a part of the first impurityregions 5017 and 5019 and the fourth impurity regions 5052 and 5057 areexposed. Conditions of this dry etching are appropriately set accordingto materials of the gate insulating film 5007, the first inorganicinsulating film 5060, and the second inorganic insulating film 5062. Inthis embodiment, since silicon oxide is used for the gate insulatingfilm 5007, silicon oxynitride is used for the first inorganic insulatingfilm 5060, and silicon nitride is used for the second inorganicinsulating film 5062. First, the second inorganic insulating film 5062consisting of silicon nitride and the first inorganic insulating film5060 consisting of silicon oxynitride are etched using CF₄, O₂, and Heas etching gases. Thereafter, the gate insulating film 5007 consistingof silicon oxide is etched using CHF₃.

Note that, at the time of this dry etching, since the first inorganicinsulating film 5060 and the second inorganic insulating film 5062 onthe first capacitor electrode 5029 are used as a dielectric body of astorage capacitor, the films are protected by a resist mask or the likeso as not to be etched.

In addition, it is essential to prevent the organic resin film 5061 frombeing exposed in the opening at the time of etching.

Next, a conductive film is formed on the second inorganic insulatingfilm 5062 so as to cover the contact hole and patterned, whereby wirings5064 to 5067 connected to the first impurity regions 5017 and 5019 andthe fourth impurity regions 5052 and 5057, a leading out wiring 5068 tobe electrically connected to an input terminal, and a second capacitorelectrode 5069 are formed. Note that a storage capacitor 5070 is formedin a part where the second capacitor electrode 5069 and the firstcapacitor electrode 5029 overlap each other with the first inorganicinsulating film 5060 and the second inorganic insulating film 5062between them in the opening of the organic resin film 5061.

Although the conductive film is shown as having a three layer structurein which a Ti film with a thickness of 100 nm, an Al film with athickness of 300 nm, and a Ti film with a thickness of 150 nm arecontinuously formed by the sputterring method on the second inorganicinsulating film 5062 in this embodiment, the present invention is notlimited to this structure. These may be formed of a conductive film witha single layer or may be formed of a conductive film with plural layersother than three layers. In addition, a material is not limited to this.

For example, these may be formed using a conductive film in which an Alfilm containing Ti is laminated after forming the Ti film or may beformed using a conductive film in which an Al film containing W islaminated after forming the Ti film.

Next, a pixel electrode 5072 being in contact with the wiring 5067 isformed by forming a transparent conductive film, for example, an ITOfilm with a thickness of 110 nm and patterning the same. The pixelelectrode 5072 is arranged so as to be in contact with and overlap thewiring 5067, whereby contact between them is realized. In addition, atransparent conductive film containing indium oxide mixed with 2 to 20%of zinc oxide (ZnO) may be used. This pixel electrode 5072 becomes ananode of the light emitting element (FIG. 16B).

Next, a photosensitive organic resin of a negative type or a positivetype is formed and a part to be opened is exposed to light, whereby asecond interlayer insulating film 5073 having an opening is formed. Notethat, a part of the pixel electrode 5072 and a part of the leading outwiring 5068 are exposed by this process.

Since roundness can be given to a section of the opening by using thephotosensitive organic resin, coverage of an electroluminescence layerand a cathode which are formed later can be made satisfactorily, and adefect called shrink in which a light emitting area decreases can bereduced.

Then, a third interlayer insulating film 5074 consisting of siliconnitride is formed on the second interlayer insulating film 5073 usingthe RF sputtering method so as to cover the exposed parts of the pixelelectrode 5072 and leading out wiring 5068. Note that the thirdinterlayer insulating film 5074 is not limited to silicon nitride, andany inorganic insulating film containing nitrogen may be used as long aspenetration of moisture shifting from the second interlayer insulatingfilm 5073 can be suppressed. For example, silicon nitride, aluminumnitride, or aluminum nitride oxide can be used.

Then, by patterning the third interlayer insulating film 5074, a part ofthe pixel electrode 5072 and a part of the leading out wiring 5068 areexposed in the opening of the second interlayer insulating film 5073.

At the time of this etching, it is essential to make an arrangement suchthat the second interlayer insulating film 5073 is not exposed in thecontact hole.

Next, the electroluminescence layer 5075 is formed by the evaporationmethod and a cathode (MgAg electrode) 5076 is further formed by theevaporation method. At this point, it is desirable to apply heattreatment to the pixel electrode 5072 prior to forming theelectroluminescence layer 5075 and the cathode 5076 and completelyremove moisture. Note that, although the MgAg electrode is used as acathode of the OLED in this embodiment, other publicly known materialsmay be used as long as it forms a conductive film with a small workfunction. For example, Ca, Al, CaF, MgAg, or AlLi may be used.

Note that AlLi is used as a cathode, Li in AlLi can be prevented fromentering the substrate side of the third interlayer insulating film 5074by the third interlayer insulating film 5074 containing nitrogen.

Here, data indicating a blocking effect of a silicon nitride film, whichis formed by the sputtering method with high frequency discharge,against lithium is shown in FIGS. 30A and 30B. FIG. 30A shows a C-Vcharacteristic of an MOS structure with a silicon nitride film formed bythe sputtering method with the high frequency discharge (represented asRF-SP SiN) as a dielectric body. Note that “Li-dip” means a solutioncontaining lithium was spin-coated on the silicon nitride film, whichmeans that the silicon nitride film was intentionally contaminated bylithium for an experiment. In addition, FIG. 30B shows a C-Vcharacteristic of an MOS structure with a silicon nitride film formed bythe plasma CVD method (represented as CVD SiN) as a dielectric body forcomparison. Note that, in data of FIG. 30B, an alloy film in whichlithium is added to aluminum as a metal electrode is used. As a resultof applying a usual BT experiment to these films (more specifically,heating treatment was performed for one hour at a temperature of ±150°C. in addition to voltage application of 1.7 MV), large change wasobserved in the C-V characteristic of the silicon nitride film formed bythe plasma CVD method and contamination by lithium was confirmed, incontrast with a result that almost no change was observed in the C-Vcharacteristic of the silicon nitride film formed by sputtering methodwith the high frequency discharge. These data indicate that the siliconnitride film formed by the sputtering method with the high frequencydischarge has a very effective blocking effect against lithiumdiffusion.

Note that a publicly known material can be used as theelectroluminescence layer 5075. Although a two layer structureconsisting of a hole transporting layer and an emitting layer isprovided as an electroluminescence layer in this embodiment, any one ofa hole injection layer, an electron injection layer, and an electrontransporting layer may be provided. In this way, various examples havebeen reported concerning a combination, and any structure of theexamples may be used.

For example, SAlq, CAlq, and the like may be used as the electrontransporting layer or the hole blocking layer.

Note that it is sufficient that a film thickness of theelectroluminescence layer 5075 is 10 to 400 nm (typically 60 to 150 nm)and a thickness of the cathode 5076 is 80 to 200 nm (typically, 100 to150 nm).

In this way, a light emitting device with a structure as shown in FIG.17A is obtained. In FIG. 17A, reference numeral 5081 denotes a pixelportion and 5082 denotes a driving circuit or other circuits. Note thata part 5080 where the pixel electrode 5072, the electroluminescencelayer 5075, and the cathode 5076 overlap each other is equivalent to theOLED.

In addition, a part of the cathode 5076 is connected to the leading outwiring 5068. The leading out wiring 5068 is electrically connected to aterminal to be connected to the FPC. A sectional structure of the partto be connected to the FPC (FPC connection part) 5083 is shown in FIG.17B.

A lead wiring 5085 formed from the same conductive layer as the gateelectrode is formed on the gate insulating film 5007. Then, the leadwiring 5085 is connected to the leading out wiring 5068 via a contacthole 5086 formed in the first inorganic insulating film 5060 and thesecond inorganic insulating film 5062 in the opening of the organicresin film 5061.

Then, on the lead wiring 5085, an opening of the organic resin film 5061is provided and the first inorganic insulating film 5060 and the secondinorganic insulating film 5062 are etched to be removed, whereby thelead wiring 5085 is exposed. Thereafter, an input terminal 5084 formedfrom the same transparent conductive film as the pixel electrode 5072 isformed on the lead wiring 5085.

A terminal of the FPC is connected to the terminal 5084 via a conductiveresin having anisotropy.

Reference numeral 5087 denotes a cover material, which is high in airtightness and is sealed by a sealing material 5088 emitting less gas.Note that, as shown in FIG. 17B, in order to increase adhesion of thecover material 5087 and the element substrate on which the lightemitting element is formed, unevenness may be provided by forming pluralopenings in the surface of the second interlayer insulating film 5073 ina part on which the sealing material 5088 is applied.

Note that the structure and the specific manufacturing method of the TFTdescribed in this embodiment are only an example, and the presentinvention is not limited to this structure.

Embodiment 2

In an active matrix semiconductor display device, a pixel portion has aplurality of pixels and a video signal is supplied through a signal lineto a pixel that is chosen by a signal inputted to a scanning line. Thisembodiment gives a description on an example in which capacitor storageis used to reduce amplitude of noise of a signal inputted from ascanning line driving circuit to the scanning line.

First, the structure of a general active matrix liquid crystal displaydevice is described. Although the description in this embodiment takesas an example a liquid crystal display device, the structure of thepresent invention is also applicable to other active matrixsemiconductor display devices.

FIG. 18A is a block diagram of a semiconductor display device of thepresent invention. Denoted by 115 is a signal line driving circuit, 116,a scanning line driving circuit, and 120, a pixel portion. The signalline driving circuit 115 has a shift register circuit 115_1, a levelshifter circuit 115_2, and a sampling circuit 115_3. In FIG. 18A, thelevel shifter circuit 115_2 is placed between the shift register circuit115_1 and the sampling circuit 115_3. Alternatively, the level shiftercircuit 115_2 may be incorporated in the shift register circuit 115_1.

As a clock signal (CLK) and a start pulse signal (SP) are supplied tothe shift register circuit 115_1, the shift register circuit 115_1generates a timing signal for controlling the timing of sampling a videosignal.

The timing signal generated is supplied to the level shifter circuit115_2. The level shifter circuit 115_2 amplifies the amplitude of thevoltage of the timing signal supplied.

The timing signal amplified by the level shifter circuit 115_2 isinputted to the sampling circuit 115_3. A video signal inputted to thesampling circuit 115_3 is sampled in sync with the timing signalinputted to the sampling circuit 115_3, and then inputted to the pixelportion 120 through a signal line.

On the other hand, the scanning line driving circuit 116 has a shiftregister circuit 117 and a buffer 118. A level shifter circuit may beadded thereto in some cases.

In the scanning line driving circuit 116, a timing signal from the shiftregister circuit 117 is inputted to the buffer 118 to be sent to acorresponding scanning line.

FIG. 18B shows a part of the pixel portion. A gate electrode of a pixelTFT 119 of every pixel in one line is connected to each scanning line.Every pixel TFT 119 in one line of pixels has to be turned onsimultaneously and therefore the buffer 118 employed has to be capableof dealing with large current flow.

In this embodiment, a capacitor structured as shown in the embodimentmode is formed between a wiring that supplies the voltage Vdd to thebuffer 118 and a scanning line. In this way, the amplitude of noise in aselection signal inputted to the scanning line is reduced.

FIG. 19 shows the structure of the buffer 118 of the scanning linedriving circuit according to this embodiment. The buffer 118 is composedof three inverters 120 to 122. The inverter 120 has an n-channel TFT 130and a p-channel TFT 131. The inverter 121 has an n-channel TFT 132 and ap-channel TFT 133. The inverter 122 has an n-channel TFT 134 and ap-channel TFT 135.

Capacitor storage 123 has two electrodes (a first capacitor electrodeand a second capacitor electrode), and one of the electrodes receivesthe power supply voltage Vdd whereas the other electrode is electricallyconnected to a scanning line.

FIG. 20A is a top view of the buffer of this embodiment which is shownin FIG. 19. FIG. 20B corresponds to a sectional view taken along theline A-A′ in FIG. 20A. A wiring 143 to which the power supply voltageVdd is supplied functions as the second capacitor electrode of thecapacitor 123. The capacitor 123 is formed in a portion where the firstcapacitor electrode 140 overlaps the wiring 143 sandwiching between afirst inorganic insulating film 141 and a second inorganic insulatingfilm 142 in an opening of an organic resin film 145.

This embodiment can be combined with Embodiment 1.

Embodiment 3

In this embodiment, a structure of a light emitting device having asectional structure different from that of the light emitting deviceshown in Embodiment 1 will be described.

In a light emitting device shown in FIG. 21A, after forming a secondinorganic insulating film 7500, a transparent conductive film is formedand patterned before forming a contact bole, whereby a pixel electrode7501 is formed. Then, a gate insulating film 7502, a first inorganicinsulating film 7503, and the second inorganic insulating film 7500 areetched in an opening of an organic resin film 7504 to form the contacthole, and a wiring 7506 electrically connecting a TFT 7505 and the pixelelectrode 7501 is formed.

In this way, by forming the pixel electrode 7501 before forming thewiring 7506, a process of polishing a surface of the pixel electrodebefore forming the wiring 7506 can be provided.

In a light emitting device shown in FIG. 21B, after forming a secondinorganic insulating film 7510, a gate insulating film 7512, a firstinorganic insulating film 7513, and the second inorganic insulating film7510 are etched in an opening of an organic resin film 7514 to form acontact hole, and a wiring 7516 electrically connecting to a TFT 7515 isformed.

Then, a second interlayer insulating film 7517 is formed covering thewiring 7516 and the second inorganic insulating film 7510. The secondinterlayer insulating film 7517 may be a positive photosensitive organicresin film or a negative photosensitive organic resin film. In FIG. 21B,the second interlayer insulating film 7517 is formed using positiveacrylic.

Then, an opening is formed in the second interlayer insulating film 7517by exposing it to light to expose a part of the wiring 7516. Thereafter,a third interlayer insulating film 7518 is formed on the secondinterlayer insulating film 7517 covering the opening, and a part of thethird interlayer insulating film 7518 is removed in the opening toexpose a part of the wiring 7516. At this point, an arrangement is madesuch that the second interlayer insulating film 7517 is not exposed inthe opening.

Then, a transparent conductive film is formed on the third interlayerinsulating film 7518 and patterned, whereby a pixel electrode 7519connected to the wiring 7516 is formed.

A light emitting device shown in FIG. 21C indicates an example in which,after forming a pixel electrode 7521 on a second inorganic insulatingfilm 7520, a third interlayer insulating film 7522 is formed usingnegative acrylic. When the third interlayer insulating film 7522 isformed using negative acrylic, it is unnecessary to perform exposurewith the object of decolorizing the third interlayer insulating film7522.

FIG. 21D illustrates an example in which the PEDOT film is removed bypatterning in case that polythiophene (PEDOT) as a hole injection layeris used in a part of an electroluminescence layer of a light emittingelement.

Since the polythiophene (PEDOT) is generally formed as a film using thespin coating method, even a part which is not desired to be formed as afilm, is formed as a film. Thus, after forming a PEDOT film 7531 on apixel electrode 7530, a light emitting layer 7532 and a cathode 7533 areformed by evaporation using a mask for evaporation. Although aparaphenylenevinylene (PPV) film is used as the light emitting layer inthis embodiment, any film may be used as long as it can be formed by theevaporation method. In addition, although Ca is used as the cathode 7533in this embodiment, any material may be used as long as it is a materialwith a small work function and can be formed by the evaporation method.

Next, PEDOT is patterned by ashing using oxygen plasma with the cathode7533 as a mask.

Next, a capacitor electrode 7534 is formed. A capacitor electrode is anelectrode provided for lowering a resistance of a cathode and consistsof a metal material having a resistance lower than that of the cathode.The capacitor electrode 7534 is obtained by forming a conductive filmconsisting of the metal material having a resistance lower than that ofthe cathode, and then patterning them.

Then, a protective film 7535 electrically connecting the capacitorelectrode 7534 and the cathode 7533 is formed by evaporation using amask for evaporation. The protective film 7535 consists of a metalmaterial, which may be the same as the material for the cathode 7533.

Note that, in FIG. 21D, an example of patterning a hole injection layerwith a cathode of a light emitting element as a mask is shown. However,this embodiment is not limited to this structure. An electroluminescencelayer other than the hole injection layer may be patterned with thecathode as a mask.

In a light emitting device shown in FIG. 22A, after forming a secondinorganic insulating film 7610, a conductive film consisting of a metalmaterial having a resistance lower than that of a cathode is formed andpatterned, whereby an capacitor electrode 7634 is formed. Then, a gateinsulating film 7612, a first inorganic insulating film 7613, and thesecond inorganic insulating film 7610 are etched in an opening of anorganic resin film 7614 to form a contact hole, and a wiring 7616electrically connecting a TFT 7615 and an capacitor electrode 7634 isformed.

The wiring 7616 is in contact with an electroluminescence layer 7617 ina part thereof and functions as a cathode.

In a light emitting device shown in FIG. 22B, after forming a cathode7700 on a second inorganic insulating film 7701, an electroluminescencelayer 7702 and an ITO film 7703 are formed. At this point, a workfunction can be reduced by adding Li to the ITO film 7703. Then, anewITO film 7704 is formed separately to cover the ITO film 7703 added withLi.

In addition, this embodiment can be conducted by combining withEmbodiment 2.

Embodiment 4

In this embodiment, electric connection between a capacitor electrodefor lowering a resistance of a cathode and an input terminal to beconnected to a terminal of an FPC will be described.

FIG. 23A shows a sectional view of a light emitting device at a pointwhen an capacitor electrode 6202 is formed on the third interlayerinsulating film 6201 after a third interlayer insulating film 6201 isformed on a second interlayer insulating film 6200 having an opening.The capacitor electrode 6202 is formed of a material having a wiringresistance lower than that of a cathode to be formed later.

Note that an electrode for FPC 6204 formed of the same conductive filmas a gate electrode 6203 of a TFT is formed in an opening of the secondinterlayer insulating film 6200. In addition, an input terminal 6205formed of the same transparent conductive film as a pixel electrode 6206is formed on the electrode for FPC 6204.

At the point of FIG. 23A, the input terminal 6205 is covered by thethird interlayer insulating film 6201 in an FPC connection part 6215.

Next, as shown in FIG. 23B, a part of the third interlayer insulatingfilm 6201 is etched to be removed, whereby the input terminal 6205 andthe pixel electrode 6206 are partly exposed. At this point, the secondinterlayer insulating film 6200 is set not to be exposed.

After laminating an electroluminescence layer 6210 and a cathode 6211 onthe pixel electrode 6206, a protective film 6212 connecting the inputterminal 6205 and the cathode 6211 is formed.

In the above-mentioned structure, when the capacitor electrode 6202 isformed by etching, since the pixel electrode 6206 is covered by thethird interlayer insulating film 6201, the surface of the pixelelectrode can be prevented from being roughened by the etching.

FIG. 24 shows a top view of a substrate (element substrate), on whichlight emitting elements are formed, of the light emitting device of thisembodiment. A state in which a pixel portion 831, scanning line drivingcircuits 832, a signal line driving circuit 833, and the input terminals6205 are formed on a substrate 830 is shown. The input terminals 6205and the respective driving circuits, a power supply line and opposedelectrodes formed in the pixel portion are connected by lead wirings835. The light emitting elements are formed the respective adjacentcapacitor electrodes 6202 which are laid out in a stripe shape.

In addition, an IC chip on which a CPU or a memory is formed may beimplemented on an element substrate by a COG (Chip on Glass) method orthe like, if necessary.

Also, this embodiment can be conducted by freely combining withEmbodiment 2.

Embodiment 5

In this embodiment, a structure of a liquid crystal display device,which is one of the semiconductor display devices of the presentinvention, will be described.

A sectional view of the liquid crystal display device of this embodimentis shown in FIG. 25. In FIG. 25, a TFT 9001 is formed on an insulatingsurface. The TFT 9001 is a top gate type and has a semiconductor film9002, a gate insulating film 9003 which is in contact with thesemiconductor film 9002, and a gate electrode 9004 which is in contactwith the gate insulating film.

On the other hand, a first capacitor electrode 9007 formed on the gateinsulating film 9003 can be formed from the same conductive film as thegate electrode 9004.

Further, a first inorganic insulating film 9008 is formed so as to coverthe TFT 9001 and the first capacitor electrode 9007. The first inorganicinsulating film 9008 is an insulating film containing nitrogen and has acharacteristic that it is less likely to penetrate moisture than anorganic resin film to be formed later.

Then, after applying a photosensitive organic resin on the firstinorganic insulating film, the photosensitive organic resin is baked anda part to be opened is exposed to light and developed, whereby anorganic resin film 9009 having the opening is formed. At this point, apart of the first inorganic resin film 9008 is exposed in the opening.

Then, a second inorganic insulating film 9010 is formed covering theorganic resin film 9009 and the part of the first inorganic insulatingfilm 9008 exposed in the opening. The second inorganic insulating film9010, like the first inorganic insulating film 9008, is an insulatingfilm containing nitrogen and has a characteristic that it is less likelyto penetrate moisture than an organic resin film to be formed later.

Then, in the opening of the organic resin film 9009, the gate insulatingfilm 9003, the first inorganic insulating film 9008, and the secondinorganic insulating film 9010 are subjected to dry etching such that apart of the semiconductor film 9002 is exposed, and a contact hole isformed. The semiconductor film 9002 has an effect as an etching stopper.

At this point, the first inorganic insulating film 9008 and the secondinorganic insulating film 9010 existing on the first capacitor electrode9007 are covered by a resist mask so as not to be etched.

Then, a conductive film is formed on the second inorganic insulatingfilm 9010 so as to cover the contact hole. The conductive film isetched, whereby wirings 9011 connected to the semiconductor film 9002and a second capacitor electrode 9012 are formed. The second capacitorelectrode 9012 overlaps the first capacitor electrode 9007 sandwichingbetween the first inorganic insulating film 9008 and the secondinorganic insulating film 9010. A storage capacitor 9013 is formed ofthe second capacitor electrode 9012, the first inorganic insulating film9008, the second inorganic insulating film 9010, and the first capacitorelectrode 9007.

Then, a transparent conductive film is formed on the second inorganicinsulating film 9010 so as to cover the wirings 9011 and the secondcapacitor electrode 9012 and patterned, whereby a pixel electrode 9015is formed. The pixel electrode 9015 is connected to one of the wirings9011 and the second capacitor electrode 9012.

Then, positive acrylic is applied on the second inorganic insulatingfilm 9010 covering the pixel electrode 9015, the wirings 9011, and thesecond capacitor electrode 9012 and baked, then partially exposed tolight and developed, whereby a third interlayer insulating film 9017having an opening is formed. Although positive acrylic is used for thethird interlayer insulating film 9017 in this embodiment, negativeacrylic may be used. The pixel electrode 9015 is exposed in the opening.The third interlayer insulating film 9017 is used as a spacer forkeeping a fixed interval between substrates. A thickness thereof isdesirably approximately 0.7 μm to several μm, although it depends upon atype of liquid crystal.

Then, an orientation film 9018 is formed. Usually, a polyimide resin isused for an orientation film for a liquid crystal display device. Afterforming the orientation film, rubbing treatment is applied to theorientation film such that liquid crystal molecules are oriented with acertain constant pre-tilt angle.

A light shielding film 9021, an opposed electrode 9022, and anorientation film 9023 are formed on an opposed substrate 9020 on anopposed side. As the light shielding film 9021, a Ti film, a Cr film, anAl film, or the like are formed with a thickness of 150 to 300 nm. Then,the pixel portion, the element substrate on which the driving circuitsare formed, and the opposed substrate are stuck together by a sealmaterial 9024. A filler (not shown) is mixed in the seal material 9024,and two substrates are stuck together with a uniform interval by thisfiller and the third interlayer insulating film 9017. Thereafter, liquidcrystal 9025 is injected between both the substrates. A publicly knownliquid crystal material can be used as a liquid crystal material. Forexample, other than TN liquid crystal, no-threshold anti-ferroelectricmixed liquid crystal showing electro-optical response property, withwhich a transmissivity continuously changes with respect to an electricfield, can also be used. Some no-threshold anti-ferroelectric mixedliquid crystal shows a V-shaped electro-optical response property. Inthis way, an active matrix liquid crystal display device shown in FIG.25 is completed.

The liquid crystal display device described in this embodiment is onlyan example of the liquid crystal devices of the present invention, andthe present invention is not limited to the structure shown in FIG. 25.

Also, this embodiment can be conducted by freely combining withEmbodiment 2.

Embodiment 6

In this embodiment, a structure of a driving circuit of a liquid crystaldisplay device, which is one of the semiconductor display devices of thepresent invention, will be described.

FIG. 26A is a schematic block diagram of an active matrix liquid crystaldisplay device of this embodiment. Reference numeral 501 denotes asignal line driving circuit; 503, a scanning line driving circuit; and504, a pixel portion.

The signal line driving circuit 501 has a shift register circuit 501-1,a latch circuit A 501-2, a latch circuit B 501-3, and a D/A conversioncircuit (DAC) 501-5. Besides, the signal line driving circuit 501 has abuffer circuit and a level shift circuit (both of which are not shown).In addition, for convenience of description, a level shift circuit isincluded in the DAC 501-5.

In addition, reference numeral 503 denotes the scanning line drivingcircuit, which may have a shift register circuit, a buffer circuit, anda level shifter circuit.

The pixel portion 504 has plural pixels. A TFT serving as a switchingelement is arranged in each pixel. One of a source and a drain of eachpixel TFT is connected to a signal line and the other is connected to apixel electrode. In addition, the gate is electrically connected to thescanning line. Each pixel TFT controls supply of a video signal to thepixel electrode electrically connected to each pixel TFT. The videosignal is supplied to each pixel electrode, a voltage is applied toliquid crystal sandwiched between each pixel electrode and an opposedelectrode to drive the liquid crystal.

First, operations of the signal line driving circuit 501 will bedescribed. In the shift register circuit 501-1, a timing signal forcontrolling timing at which a digital video signal is latched by thelatch circuit A 501-2 is generated based upon an inputted clock signaland a start pulse.

In the latch circuit A 501-2, the digital video signal is latchedsynchronizing with the generated timing signal. When the digital videosignal is latched in all stages of the latch circuit A 501-2, a latchsignal is supplied to the latch circuit B 501-3 in accordance withoperation timing of the shift register circuit 501-1. At this instance,the digital video signal latched by the latch circuit A 501-2 istransmitted to the latch circuit B 501-3 all at once and latched bylatch circuits of all the stages of the latch circuit B 501-3.

In the latch circuit A 501-2 which has completed transmitting thedigital video signal to the latch circuit B 501-3, the digital videosignal is latched sequentially based upon a timing signal from the shiftregister circuit 501-1.

On the other hand, the digital video signal latched in the latch circuitB 501-3 is supplied to the D/A conversion circuit (DAC) 501-5. The DAC501-5 converts the digital video signal into an analog video signal andsupplies the analog signal to each signal line sequentially.

In the scanning line driving circuit 503, a timing signal from a shiftregister circuit (not shown) is supplied to a buffer circuit (not shown)and to a corresponding scanning line. Since gate electrodes of pixelTFTs for one line are connected to the scanning line and all the pixelTFTs for one line have to be turned ON simultaneously, a buffer circuitwith a large current capacity is used for the above-mentioned buffercircuit.

In this way, switching of a corresponding pixel TFT is performed by ascanning signal from the scanning line driving circuit, an analog videosignal (gradation voltage) from the signal line driving circuit issupplied to the pixel TFT to drive liquid crystal molecules.

In the liquid crystal display device of this embodiment, in case thatthe D/A conversion circuit 501-5 is a capacity dividing type, it mayhave a capacitor of the structure described in the embodiment mode.

Note that, although the signal line driving circuit and the scanningline driving circuit described in this embodiment are used as drivingcircuits of a liquid crystal display device, the driving circuits may beused as driving circuits of a light emitting device or othersemiconductor display devices.

Embodiment 7

The semiconductor display device manufactured by the present inventioncan be applied to various electronic apparatuses. Examples of theelectronic apparatuses can be given as portable information terminals(electronic books, mobile computers, cellular phones, or the like),video cameras, digital cameras, personal computers, TV receivers,cellular phones, projection display apparatuses, or the like. Specificexamples of these electronic apparatuses are shown in FIGS. 27A to 27H.

FIG. 27A shows a display device including a case 2001, a support base2002, a display unit 2003, speaker units 2004, a video input terminal2005, etc. The display device of the present invention is completed byusing the semiconductor display device of the present invention to thedisplay unit 2003. The display device refers to all display devices fordisplaying information, including ones for personal computers, for TVbroadcasting reception, and for advertisement.

FIG. 27B shows a digital still camera including a main body 2101, adisplay unit 2102, an image receiving unit 2103, operation keys 2104, anexternal connection port 2105, a shutter 2106, etc. The digital stillcamera of the present invention is completed by using the semiconductordisplay device of the present invention to the display unit 2102.

FIG. 27C shows a note-type personal computer including a main body 2201,a case 2202, a display unit 2263, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, etc. The laptop of thepresent invention is completed by using the semiconductor display deviceof the present invention to the display unit 2203.

FIG. 27D shows a mobile computer including a main body 2301, a displayunit 2302, a switch 2303, operation keys 2304, an infrared port 2305,etc. The mobile computer of the present invention is completed by usingthe semiconductor display device of the present invention to the displayunit 2302.

FIG. 27E shows a portable image reproducing apparatus having a recordingmedium (a DVD player, to be specific). The apparatus includes a mainbody 2401, a case 2402, a display unit A 2403, a display unit B 2404, arecording medium (DVD or the like) reading unit 2405, operation keys2406, speaker units 2407, etc. The display unit A 2403 mainly displaysimage information whereas the display unit B 2404 mainly displays textinformation. Domestic video games and the like are also included in theimage reproducing apparatus having a recording medium. The portableimage reproducing apparatus of the present invention is completed byusing the semiconductor display device of the present invention to thedisplay units A 2403 and B 2404.

FIG. 27F shows a goggle type display (head mounted display) including amain body 2501, display units 2502, and arm units 2503. The goggle typedisplay of the present invention is completed by using the semiconductordisplay device of the present invention to the display units 2502.

FIG. 27G shows a video camera including a main body 2601, a display unit2602, a case 2603, an external connection port 2604, a remote controlreceiving unit 2605, an image receiving unit 2606, a battery 2607, anaudio input unit 2608, operation keys 2609, eye piece portion 2610 etc.The video camera of the present invention is completed by using thesemiconductor display device of the present invention to the displayunit 2602.

FIG. 27H shows a cellular phone including a main body 2701, a case 2702,a display unit 2703, an audio input unit 2704, an audio output unit2705, operation keys 2706, an external connection port 2707, an antenna2708, etc. The display unit 2703 displays white letters on a blackbackground, therefore the cellular phone consumes less power. Thecellular phone of the present invention is completed by using thesemiconductor display device of the present invention to the displayunit 2703.

As described above, the application range of the present invention is sowide that can be applied to electronic apparatuses in any field. Thisembodiment can be conducted by combining with any configuration shown inEmbodiments 1 to 6.

Embodiment 8

A photograph shown in FIG. 31A is a sectional SEM (scanning electronmicroscope) photograph in a state in which dry etching treatment isapplied to a non-photosensitive acrylic film (film thickness:approximately 1.3 μm) to pattern it. FIG. 31B is a schematic view ofFIG. 31A. When the dry etching treatment is applied to thenon-photosensitive acrylic film as in the past, a curved surface ishardly formed in an upper part of the pattern, and an upper endsubstantially without a curvature radius (R) is obtained. In addition,although a taper angle (contact angle) is approximately 63° in a lowerpart of the pattern, no curved surface is observed in this lower endeither.

Next, a photograph shown in FIG. 32A is a sectional SEM photograph in astate in which exposure and development treatment are applied to apositive photosensitive acrylic film (film thickness: approximately 2.0μm) to pattern it. FIG. 32B is a schematic view of FIG. 32A. A sectionalshape of the positive photosensitive acrylic film has an extremelygentle curved surface after etching treatment with a developer, and acurvature radius (R) changes continuously. In addition, as a contactangle, a value as small as approximately 32 to 33° is obtained. That is,it is just like the shape shown in FIG. 1B. It can be said that it is avery useful shape in manufacturing the thin film transistor and thesemiconductor display device of the present invention. It is needless tomention that, although a value of the contact angle changes dependingupon etching conditions, a film thickness, and the like, it only has tosatisfy 30°<θ<65° as described above.

Next, a photograph shown in FIG. 33A is a sectional SEM photograph in astate in which exposure and development treatment are applied to anegative photosensitive acrylic film (film thickness: approximately 1.4μm) to pattern it. FIG. 33B is a schematic view of FIG. 33A. A sectionalshape of the negative photosensitive acrylic film has a gentle S-shapedcurved surface after etching treatment with a developer and is curvedwith a certain curvature radius (R) in an upper end of the pattern. Inaddition, as a contact angle, a value of approximately 47° is obtained.In this case, a length of a part of a tail represented by W in FIG. 33Bis a problem. In particular, in a contact hole (opening) requiring finemachining, if this tail part becomes long, it is likely that a state inwhich an electrode or a wiring in a lower layer is not exposed in thecontact hole occurs, and disconnection due to contact failure is feared.However, a possibility of such disconnection decreases if the length (W)of this tail part is 1 μm or less (preferably, a length less than aradius of the contact hole).

Next, a photograph shown in FIG. 34A is a sectional SEM photograph in astate in which exposure and development treatment are applied to apositive photosensitive polyimide film (film thickness: approximately1.5 μm) to pattern it. FIG. 34B is a schematic view of FIG. 33A. Asectional shape of the positive photosensitive polyimide film has aslight tail part (represented by a length W) and a curved upper endafter etching treatment with a developer. However, a certain curvatureradius (R) thereof is small.

Observing the above-mentioned sectional shapes, considerations asdescribed blow can be made. After forming a contact hole (opening), whena metal film to be an electrode or a wiring is formed, the sputteringmethod, the evaporation method, or the CVD method is used. It is knownthat, when material molecules constituting a thin film deposit on asurface to be formed, the material molecules move on the surface to finda stable site, and tend to gather in a part of a shape having an acuteangle (shape to be a convex part) like an upper end of the contact hole.In particular, this tendency is conspicuous in the evaporation method.Thus, when a sectional shape of the opening is the shape as shown inFIG. 31A, since the material molecules concentrate on the edge of theopening, a film thickness increases in that part locally and a projectedpart of an eave shape is formed. This projected part is not preferablebecause it becomes a cause of a failure such as disconnection (stepbreakage) later. Therefore, it can be said that the non-photosensitiveacrylic film shown in FIG. 31A and the positive photosensitive polyimidefilm shown in FIG. 34A are materials disadvantageous from the viewpointof a coverage.

In addition, in the shape with the tail part formed in the lower end ofthe contact hole as shown in FIGS. 33A and 34A, it is likely that thetail part may cover the bottom surface of the contact hole to causeconnection failure according to circumstances. Therefore, it can be saidthat the films having such a shape is a disadvantageous material fromthe viewpoint of a contact property. It is needless to mention thatthere is no problem if the length of the tail part is 1 μm or less(preferably, a length less than the radius of the contact hole).

Embodiment 9

This embodiment gives a description on a method of manufacturing asemiconductor display device of the present invention. In thisembodiment, a partial sectional structure in each step is shown for aportion 9200 to be connected with an FPC (FPC connection portion), afirst capacitor electrode 9222, a pixel portion 9220, and a protectivecircuit 9201.

First, a TFT 9202 is formed on a substrate and a lead wiring 9221 isformed on a gate insulating film 9204. The TFT 9202 has a semiconductorfilm 9203, the gate insulating film 9204 that is in contact with thesemiconductor film 9203, and a gate electrode 9205 that is in contactwith the gate insulating film 9204. The lead wiring 9221 and the firstcapacitor electrode 9222 are formed from the same conductive film as thegate electrode 9205.

This embodiment uses SiON for the gate insulating film 9204. For amethod of forming the gate insulating film and its thickness, see thedescription in Embodiment 1.

A first inorganic insulating film 9206 is formed to cover the leadwiring 9221, the first capacitor electrode 9222, and the TFT 9202. Thisembodiment uses SiN for the first inorganic insulating film 9206. For amethod of forming the first inorganic insulating film 9206 and itsthickness, see the description in Embodiment 1.

In this embodiment, the first inorganic insulating film 9206 is coveredwith a barrier film 9207 (FIG. 35A). The barrier film 9207 in thisembodiment is formed of SiO₂ by CVD to a thickness of approximately 30to 120 nm.

Next, organic resin is applied to the top face of the barrier film 9207.The organic resin film is partially exposed to light and developed toobtain an organic resin film 9208 with openings (FIG. 35B). The organicresin film 9208 may be bleached by exposing the entirety to light afterpartial exposure to light and before development as described inEmbodiment 1.

Using the organic resin film 9208 as a mask, the barrier film 9207formed of SiO₂ is subjected to wet etching. In this embodiment, the wetetching uses a hydrofluoric acid-based etchant and the temperature isset to 20° C. to remove the barrier film 9207 from the openings of theorganic resin film 9208, thereby exposing the first inorganic insulatingfilm 9206 in the openings of the organic resin film 9208 (FIG. 35C).

A second inorganic insulating film 9209 is formed from SiN on theorganic resin film 9208 so as to cover the openings. For a method offorming the second inorganic insulating film 9209 and its thickness, seethe description in Embodiment 1.

The first inorganic insulating film 9206, the second inorganicinsulating film 9209, and the gate insulating film 9204 are subjected todry etching to form contact holes in the openings of the organic resinfilm 9208. The lead wiring 9221 and impurity regions 9225 and 9226 ofthe semiconductor film 9203 are partially exposed in the contact holes.During the dry etching, the first capacitor electrode 9222 is coveredwith a mask to avoid exposure.

Then a conductive film is formed on the second inorganic insulating film9209 covering the contact holes and is patterned to form a leading outwiring 9210, a wiring 9211, and a second capacitor electrode 9212. Theleading out wiring 9210 is in contact with the lead wiring 9221. Thewiring 9211 is in contact with the impurity region 9226 of thesemiconductor film 9203. The second capacitor electrode 9212 overlapsthe first capacitor electrode 9222 in the opening of the organic resinfilm 9208 sandwiching between the first inorganic insulating film 9206and the second inorganic insulating film 9209 are interposed between thecapacitor electrodes.

Then a transparent conductive film is formed and patterned to form aninput terminal 9213 adjacent to the lead wiring 9221 in the contact holeand a pixel electrode 9224 adjacent to the wiring 9211.

The first inorganic insulating film 9206 formed of SiN has higherelectric conductivity than the barrier film 9207 formed of SiO₂.Therefore, so-called charging damage in which holes are trapped in thegate insulating film 9204 is prevented even though the films are exposedto plasma atmosphere during dry etching for forming the contact holes.Fluctuation of TFT threshold toward the plus side is thus prevented.

This embodiment can be combined freely with Embodiments 1 through 8.

Embodiment 10

This embodiment explains variations of step order after a contact holeis formed in first and second inorganic insulating films in a method ofmanufacturing a semiconductor display device of the present invention.

In FIG. 37A, a lead wiring 9104 is formed on a gate insulating film 9103in an FPC connection portion 9100. A TFT 9101 is formed in a pixelportion 9120. The TFT 9101 has a semiconductor film 9102, a gateinsulating film 9103 adjacent to the semiconductor film 9102, and a gateelectrode 9121 adjacent to the gate insulating film 9103. A firstinorganic insulating film 9105 is formed to cover the lead wiring 9104and the TFT 9101. An organic resin film 9106 having an opening is formedon the first inorganic insulating film 9105. A second inorganicinsulating film 9107 is formed on the organic resin film 9106 coveringthe opening.

A contact hole is formed through the first inorganic insulating film9105 and the second inorganic insulating film 9107 in the opening of theorganic resin film 9106. The lead wiring 9104 and impurity regions ofthe semiconductor film 9102 are partially exposed in the contact hole.

Next, a transparent conductive film 9108 is formed on the secondinorganic insulating film 9107 to cover the contact hole as shown inFIG. 37B.

The transparent conductive film 9108 is patterned as shown in FIG. 37Cto form an input terminal 9109 adjacent to the lead wiring 9104 in thecontact hole and a pixel electrode 9110.

Next, a conductive film is formed and patterned to form a lead wiring9111 and a wiring 9112. The lead wiring 9111 is adjacent to the leadwiring 9104 in the contact hole. The wiring 9112 is adjacent to theimpurity regions of the semiconductor film 9102 and with the pixelelectrode.

A step of polishing the surface of the transparent conductive film 9108or the pixel electrode 9110 is added to FIGS. 37A to 37D. The surfacepolishing can be put after formation of the transparent conductive film9108 and before patterning thereof, namely, between FIG. 37B and FIG.37C. Alternatively, the surface polishing may be put after formation ofthe pixel electrode 9110 by patterning and before formation of thewiring, namely, between FIG. 37C and FIG. 37D. Since the wiring is notformed yet, the surface of the transparent conductive film 9108 or thepixel electrode 9110 alone is polished by the above surface polishing.

It is also possible to put the surface polishing after the wiring 9112is formed, namely, after FIG. 37D. This prevents fine particles, whichis resulted from the surface polishing of the transparent conductivefilm or the pixel electrode, from entering into the contact hole,thereby preventing contact defects.

The description given next is about a method of manufacturing asemiconductor display device of the present invention which has adifferent manufacture step order from the one illustrated in FIGS. 37Ato 37D.

In FIG. 38A, a lead wiring 9004 is formed on a gate insulating film 9003in an FPC connection portion 9000. A TFT 9001 is formed in a pixelportion 9020. The TFT 9001 has a semiconductor film 9002, a gateinsulating film 9003 adjacent to the semiconductor film 9002, and a gateelectrode 9021 adjacent to the gate insulating film 9003. A firstinorganic insulating film 9005 is formed to cover the lead wiring 9004and the TFT 9001. An organic resin film 9006 having an opening is formedon the first inorganic insulating film 9005. A second inorganicinsulating film 9007 is formed on the organic resin film 9006 coveringthe opening.

A contact hole is formed through the first inorganic insulating film9005 and the second inorganic insulating film 9007 in the opening of theorganic resin film 9006. The lead wiring 9004 and impurity regions ofthe semiconductor film 9002 are partially exposed in the contact hole.

Then as shown in FIG. 38B, a conductive film is formed so as to coverthe contact hole and is patterned to form a lead wiring 9011 and awiring 9008. The lead wiring 9011 is adjacent to the lead wiring 9004 inthe contact hole. The wiring 9008 is adjacent to the impurity regions ofthe semiconductor film 9002.

Next, a transparent conductive film 9010 is formed as shown in FIG. 38C.The transparent conductive film 9010 is adjacent to the lead wiring 9004in the contact hole. The transparent conductive film 9010 is alsoadjacent to the wiring 9008.

The transparent conductive film 9010 is then patterned as shown in FIG.38D to form an input terminal 9013 adjacent to the lead wiring 9004 anda pixel electrode 9012 that is adjacent to the wiring 9008.

The process shown in FIGS. 38A to 38D has a step of polishing thesurface of the transparent conductive film 9010 or the pixel electrode9013. The surface polishing can be put after formation of thetransparent conductive film 9010 and before patterning thereof, namely,between FIG. 38C and FIG. 38D. Alternatively, the surface polishing maybe put after the pixel electrode 9013 is formed by patterning, namely,after FIG. 38D. This prevents fine particles, which is resulted from thesurface polishing of the transparent conductive film or the pixelelectrode, from entering into the contact hole, thereby preventingcontact defects.

If an ITO film is formed on an acrylic resin film, the ITO film is insome cases peeled off of the acrylic resin film upon polishing of theITO film. The peeling of the ITO film upon polishing can be prevented byforming an inorganic insulating film between the acrylic resin film andthe ITO film.

This embodiment can be combined freely with Embodiments 1 through 9.

While various embodiments in accordance with the present invention havebeen shown and described, it is understood that the invention is notlimited thereto. The present invention may be changed, modified andfurther applied by those skilled in the art. Therefore, this inventionis not limited to the detail shown and described previously, but alsoincludes all such changes and modifications.

1. A semiconductor device having a protective circuit, the protectivecircuit comprising: a first capacitor electrode formed over a substrate;a first inorganic insulating film formed over the first capacitorelectrode; an organic resin film formed over the first inorganicinsulating film; an opening formed in the organic resin film; a secondinorganic insulating film formed over the organic resin film and incontact with the first inorganic insulating film in the opening; and asecond capacitor electrode formed over the second inorganic insulatingfilm, wherein the radius of curvature on a surface of the organic resinfilm is continuously lengthened as the distance from the opening isincreased.
 2. A semiconductor display device according to claim 1,wherein the protective circuit rectifies the waveform of a signal.
 3. Asemiconductor display device according to claim 1, wherein the organicresin film comprises an acrylic film.
 4. A semiconductor display deviceaccording to claim 1, wherein each of the first and second inorganicinsulating films is selected from the group consisting of a siliconnitride film, a silicon oxynitride film, and an aluminum oxynitridefilm.
 5. A semiconductor display device according to claim 1, whereinthe protective circuit further comprises a resistor.
 6. An electronicapparatus having the semiconductor display device according to claim 1,wherein the electronic apparatus is selected from the group consistingof a portable information terminal, an electronic book, a mobilecomputer, a video camera, a digital camera, a personal computer, a TVreceiver, a cellular phone, and a projection display apparatus.
 7. Asemiconductor device having a protective circuit, the protective circuitcomprising: a first capacitor electrode formed over a substrate; a firstinorganic insulating film formed over the first capacitor electrode; anorganic resin film formed over the first inorganic insulating film; anopening formed in the organic resin film; a second inorganic insulatingfilm formed over the organic resin film and in contact with the firstinorganic insulating film in the opening; and a second capacitorelectrode formed over the second inorganic insulating film, wherein anedges of the opening on a surface of the organic resin film has insection a parabolic shape whose principal axis is in a plane parallel tothe substrate.
 8. A semiconductor display device according to claim 7,wherein the protective circuit rectifies the waveform of a signal.
 9. Asemiconductor display device according to claim 7, wherein the organicresin film comprises an acrylic film.
 10. A semiconductor display deviceaccording to claim 7, wherein each of the first and second inorganicinsulating films is selected from the group consisting of a siliconnitride film, a silicon oxynitride film, and an aluminum oxynitridefilm.
 11. A semiconductor display device according to claim 7, whereinthe protective circuit further comprises a resistor.
 12. An electronicapparatus having the semiconductor display device according to claim 7,wherein the electronic apparatus is selected from the group consistingof a portable information terminal, an electronic book, a mobilecomputer, a video camera, a digital camera, a personal computer, a TVreceiver, a cellular phone, and a projection display apparatus.
 13. Asemiconductor device comprising: a pixel portion formed over asubstrate; an input terminal fonned over the substrate; a protectivecircuit formed over the substrate; a lead wiring formed over thesubstrate wherein the pixel portion is operationally connected to theinput terminal through at least the protective circuit and the leadwiring, the protective circuit comprising: a first capacitor electrodeformed over the substrate; a first inorganic insulating film formed overthe first capacitor electrode; an organic resin film formed over thefirst inorganic insulating film; an opening formed in the organic resinfilm; a second inorganic insulating film formed over the organic resinfilm and in contact with the first inorganic insulating film in theopening; and a second capacitor electrode formed over the secondinorganic insulating film, wherein the radius of curvature on a surfaceof the organic resin film is continuously lengthened as the distancefrom the opening is increased.
 14. A semiconductor display deviceaccording to claim 13, wherein the organic resin film comprises anacrylic film.
 15. A semiconductor display device according to claim 13,wherein each of the first and second inorganic insulating films isselected from the group consisting of a silicon nitride film, a siliconoxynitride film, and an aluminum oxynitride film.
 16. A semiconductordisplay device according to claim 13, wherein the protective circuitfurther comprises a resistor.
 17. An electronic apparatus having thesemiconductor display device according to claim 13, wherein theelectronic apparatus is selected from the group consisting of a portableinformation terminal, an electronic book, a mobile computer, a videocamera, a digital camera, a personal computer, a TV receiver, a cellularphone, and a projection display apparatus.
 18. A semiconductor devicecomprising: a pixel portion formed over a substrate; an input terminalformed over the substrate; a protective circuit formed over thesubstrate; a lead wiring formed over the substrate wherein the pixelportion is operationally connected to the input terminal through atleast the protective circuit and the lead wiring, the protective circuitcomprising: a first capacitor electrode formed over a substrate; a firstinorganic insulating film formed over the first capacitor electrode; anorganic resin film formed over the first inorganic insulating film; anopening formed in the organic resin film; a second inorganic insulatingfilm formed over the organic resin film and in contact with the firstinorganic insulating film in the opening; and a second capacitorelectrode formed over the second inorganic insulating film, wherein anedge of the opening on a surface of the organic resin film has insection a parabolic shape whose principal axis is in a plane parallel tothe substrate.
 19. A semiconductor display device according to claim 18,wherein the organic resin film comprises an acrylic film.
 20. Asemiconductor display device according to claim 18, wherein each of thefirst and second inorganic insulating films is selected from the groupconsisting of a silicon nitride film, a silicon oxynitride film, and analuminum oxynitride film.
 21. A semiconductor display device accordingto claim 18, wherein the protective circuit further comprises aresistor.
 22. An electronic apparatus having the semiconductor displaydevice according to claim 18, wherein the electronic apparatus isselected from the group consisting of a portable information terminal,an electronic book, a mobile computer, a video camera, a digital camera,a personal computer, a TV receiver, a cellular phone, and a projectiondisplay apparatus.